U.S. patent number 11,136,239 [Application Number 16/413,746] was granted by the patent office on 2021-10-05 for methods for forming nanotube fabrics with controlled surface roughness and degree of rafting.
The grantee listed for this patent is Nantero, Inc.. Invention is credited to Jennifer Black, Joseph James McDermott, David A. Roberts, Rahul Sen, Billy Smith.
United States Patent |
11,136,239 |
McDermott , et al. |
October 5, 2021 |
Methods for forming nanotube fabrics with controlled surface
roughness and degree of rafting
Abstract
Methods for forming a nanotube fabric with a controlled surface
roughness (or smoothness) and a selected degree of rafting are
disclosed by adjusting the concentration levels of a selected ionic
species within a nanotube formulation used to form the nanotube
fabric. In one aspect, the present disclosure provides a nanotube
formulation roughness curve (and methods for generating such a
curve) that can be used to select a utilizable range of ionic
species concentration levels that will provide a nanotube fabric
with a desired surface roughness (or smoothness) and degree of
rafting. In some aspects of the present disclosure, such a nanotube
formulation roughness curve can be used adjust nanotube formulation
prior to a nanotube formulation deposition process to provide
nanotube fabrics that are relatively smooth with a low degree of
rafting.
Inventors: |
McDermott; Joseph James
(Watertown, MA), Black; Jennifer (Woburn, MA), Sen;
Rahul (Lexington, MA), Roberts; David A. (Woburn,
MA), Smith; Billy (Woburn, MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nantero, Inc. |
Woburn |
MA |
US |
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Family
ID: |
67984804 |
Appl.
No.: |
16/413,746 |
Filed: |
May 16, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190292057 A1 |
Sep 26, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15483614 |
Apr 10, 2017 |
10773960 |
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13578691 |
Apr 11, 2017 |
9617151 |
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PCT/US2011/024710 |
Feb 14, 2011 |
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61304045 |
Feb 12, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B82Y
30/00 (20130101); H01B 1/04 (20130101); C01B
32/158 (20170801); B82Y 40/00 (20130101); C01B
32/168 (20170801); Y10S 977/751 (20130101); Y10S
977/752 (20130101); G11C 13/025 (20130101); Y10T
428/249921 (20150401); C01B 2202/02 (20130101); C01B
2202/34 (20130101); C01B 2202/06 (20130101); C01B
2202/22 (20130101); C01B 2202/36 (20130101) |
Current International
Class: |
B82Y
30/00 (20110101); B82Y 40/00 (20110101); H01B
1/04 (20060101); C01B 32/158 (20170101); G11C
13/02 (20060101) |
Field of
Search: |
;252/500,502,510,511 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Goh "Surfactant dispersed multi-walled carbon
nanotube/polyetherimide nanocomposite membrane." Solid State
Sciences 12 (2010) 2155-2162 (Year: 2012). cited by
examiner.
|
Primary Examiner: Nguyen; Tri V
Attorney, Agent or Firm: Kenja IP Law PC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent
application Ser. No. 15/483,614 (now US Patent Publication No. US
2017/0210626), entitled "Low Porosity Nanotube Fabric Articles,"
and filed Apr. 10, 2017, which is a continuation of U.S. patent
application Ser. No. 13/578,691 (now U.S. Pat. No. 9,617,151),
entitled "Methods for Controlling Density, Porosity, and/or Gap
Size within Nanotube Fabric Layers and Films, filed Oct. 31, 2012,
which is a U.S. National Phase application under 35 U.S.C. .sctn.
371 of International Patent Application No. PCT/US2011/024710 filed
on Feb. 14, 2011, entitled "Methods for Controlling Density,
Porosity, and/or Gap Size within Nanotube Fabric Layers and Films,"
which claims priority under 35 U.S.C. .sctn. 119(e) to U.S.
Provisional Patent Application No. 61/304,045, filed Feb. 12, 2010,
which is incorporated by reference its entirety. This application
is also related to the following U.S. patents, which are assigned
to the assignee of the present application, and are hereby
incorporated by reference in their entirety:
Methods of Nanotube Films and Articles (U.S. Pat. No. 6,835,591),
filed Apr. 23, 2002;
Methods of Using Pre-Formed Nanotubes to Make Carbon Nanotube
Films, Layers, Fabrics, Ribbons, Elements, and Articles (U.S. Pat.
No. 7,335,395), filed Jan. 13, 2003;
Devices Having Horizontally-Disposed Nanofabric Articles and
Methods of Making the Same (U.S. Pat. No. 7,259,410), filed Feb.
11, 2004;
Devices Having Vertically-Disposed Nanofabric Articles and Methods
of Making Same (U.S. Pat. No. 6,924,538), filed Feb. 11, 2004;
Resistive Elements Using Carbon Nanotubes (U.S. Pat. No.
7,365,632), filed Sep. 20, 2005; and
Spin-Coatable Liquid for Formation of High Purity Nanotube Films
(U.S. Pat. No. 7,375,369), filed Jun. 3, 2004.
This application is related to the following patent applications,
which are assigned to the assignee of the application, and are
hereby incorporated by reference in their entirety:
Methods of Making Carbon Nanotube Films, Layers, Fabrics, Ribbons,
Elements, and Articles (U.S. patent application Ser. No.
10/341,005), filed Jan. 13, 2003;
High Purity Nanotube Fabrics and Films (U.S. patent application
Ser. No. 10/860,332), filed Jun. 3, 2004;
Aqueous Carbon Nanotube Applicator Liquids and Methods for
Producing Applicator Liquids Thereof (U.S. patent application Ser.
No. 11/304,315), filed Dec. 15, 2005; and
Anisotropic Nanotube Fabric Layers and Films and Methods of Forming
Same (U.S. patent application Ser. No. 12/533,687), filed Jul. 31,
2009.
Claims
What is claimed is:
1. A method of forming a nanotube fabric, comprising: suspending a
volume of nanotubes within a liquid medium; processing and
purifying said suspension of nanotubes to realize a nanotube
formulation; selecting at least one ionic species to use within
said nanotube formulation; selecting at least one of a surface
roughness threshold and a degree of rafting threshold for said
nanotube fabric; characterizing said nanotube formulation and using
said nanotube formulation characterization to select a target
concentration level for said at least one ionic species within said
nanotube formulation; adjusting said nanotube formulation to form
an adjusted nanotube formulation that includes said selected at
least one ionic species at said target concentration level; and
depositing said adjusted nanotube formulation via a spin coating
operation to form a nanotube fabric.
2. The method of claim 1 wherein said nanotubes within said volume
of nanotubes have at least one preselected parameter.
3. The method of claim 2 wherein said at least one preselected
parameter includes at least one of length, length distribution,
degree of straightness, nanotube wall type, chirality, and
functionalization.
4. The method of claim 3 wherein said nanotube wall type is one of
singled walled, doublewalled, multi-walled, or a preselected
mixture thereof.
5. The method of claim 1 wherein said nanotubes are carbon
nanotubes.
6. The method of claim 1 wherein said nanotube formulation
characterization includes defining a utilization range of
concentration levels for said at least one selected ionic
species.
7. The method of claim 6 wherein said utilization range corresponds
to desired characteristics within said nanotube fabric.
8. The method of claim 7 wherein said desired characteristics
include at least one of surface roughness and degree of
rafting.
9. The method of claim 8 wherein said desired characteristics
include a surface roughness less than a preselected threshold
value.
10. The method of claim 8 wherein said desired characteristics
include a degree of rafting less than a preselected threshold
value.
11. The method of claim 1 wherein said at least one ionic species
is selected from the list consisting of ammonium salts, nitrate
salts, ammonium nitrate salts, ammonium formate, ammonium acetate,
ammonium carbonate, ammonium bicarbonate, ionic organic species,
ionic polymers, and inorganic salts.
12. The method of claim 1 where said at least one ionic species
includes a cation component selected from the list consisting of
ammonium, tetraalkylammoniums, acids of primary aliphatic amines,
acids of secondary aliphatic amines, acids of tertiary aliphatic
amines, acids of cylic amines, cylic aromatic quaternary amines,
and phosphorus-based ions.
13. The method of claim 1 where said at least one ionic species
includes an anion component selected from the list consisting of
soluble organic acid bases, simple soluble aliphatic carboxylic
acids, complex organic acids, nitrate, phosphate, sulfate, and
carbonate.
Description
TECHNICAL FIELD
The present disclosure relates generally to nanotube fabric layers
and films and, more specifically, to a method of controlling
density, porosity and/or gap size within nanotube fabric layers and
films.
BACKGROUND
Any discussion of the related art throughout this specification
should in no way be considered as an admission that such art is
widely known or forms part of the common general knowledge in the
field.
Nanotube fabric layers and films are used in a plurality of
electronic structures, and devices. For example, U.S. patent
application Ser. No. 11/835,856 to Bertin et al., incorporated
herein by reference in its entirety, teaches methods of using
nanotube fabric layers to realize nonvolatile devices such as, but
not limited to, block switches, programmable resistive elements,
and programmable logic devices. U.S. Pat. No. 7,365,632 to Bertin
et al., incorporated herein by reference, teaches the use of such
fabric layers and films within the fabrication of thin film
nanotube based resistors. U.S. patent application Ser. No.
12/066,063 to Ward et al., incorporated herein by reference in its
entirety, teaches the use of such nanotube fabrics and films to
form heat transfer elements within electronic devices and
systems.
Through a variety of previously known techniques (described in more
detail within the incorporated references) nanotube elements can be
rendered conducting, non-conducting, or semi-conducting before or
after the formation of a nanotube fabric layer or film, allowing
such nanotube fabric layers and films to serve a plurality of
functions within an electronic device or system. Further, in some
cases the electrical conductivity of a nanotube fabric layer or
film can be adjusted between two or more non-volatile states as
taught in U.S. patent application Ser. No. 11/280,786 to Bertin et
al., incorporated herein by reference in its entirety, allowing for
such nanotube fabric layers and films to be used as memory or logic
elements within an electronic system.
U.S. Pat. No. 7,334,395 to Ward et al., incorporated herein by
reference in its entirety, teaches a plurality of methods for
forming nanotube fabric layers and films on a substrate element
using preformed nanotubes. The methods include, but are not limited
to, spin coating (wherein a solution of nanotubes is deposited on a
substrate which is then spun to evenly distribute said solution
across the surface of said substrate), spray coating (wherein a
plurality of nanotube are suspended within an aerosol solution
which is then dispersed over a substrate), and dip coating (wherein
a plurality of nanotubes are suspended in a solution and a
substrate element is lowered into the solution and then removed).
Further, U.S. Pat. No. 7,375,369 to Sen et al., incorporated herein
by reference in its entirety, and U.S. patent application Ser. No.
11/304,315 to Ghenciu et al., incorporated herein by reference in
its entirety, teach nanotube solutions well suited for forming a
nanotube fabric layer over a substrate element via a spin coating
process.
SUMMARY OF THE DISCLOSURE
The current disclosure relates to a method for controlling density,
porosity and/or gap size within nanotube fabric layers and
films.
In particular, the present disclosure provides a nanotube fabric
layer including a plurality of individual nanotube elements where
open regions between said individual nanotube elements within the
nanotube fabric layer define gaps within said nanotube fabric layer
and where the gaps are limited in physical dimension to be smaller
than a threshold. In some embodiments, a nanotube switching device
includes such a nanotube fabric layer.
The present disclosure also provides a nanotube fabric layer
including a plurality of individual nanotube elements where open
regions between said individual nanotube elements within said
nanotube fabric layer define a porosity of said nanotube fabric
layer and where said porosity is selected to provide a uniform
density of individual nanotube elements within the nanotube fabric
layer. In some embodiments, the nanotube fabric layer has a high
porosity. In some embodiments, the nanotube fabric layer has a low
porosity. In some embodiments, a nanotube switching device includes
such a nanotube fabric layer.
The present disclosure also provides a method of preparing a
nanotube application solution. The method first includes forming a
raw nanotube application solution, this raw nanotube application
solution comprising a first plurality of nanotube elements at a
first concentration level and a second plurality of ionic particles
at a second concentration level dispersed in a liquid medium. The
method further includes adjusting at least one of the first
concentration level of the first plurality of nanotube elements and
the second concentration level of the second quantity of ionic
particles such as to control the degree of rafting realized within
a nanotube fabric layer formed using the nanotube application
solution.
According to one aspect of the present disclosure, the first
plurality of nanotube elements are carbon nanotubes.
Under another aspect of the present disclosure, the first plurality
of nanotube elements are single walled carbon nanotubes.
Under another aspect of the present disclosure, the first plurality
of nanotube elements are multi-walled carbon nanotubes.
Under another aspect of the present disclosure, the second
plurality of ionic particles include ammonium nitrate salts.
Under another aspect of the present disclosure, the second
plurality of ionic particles include ammonium formate.
Under another aspect of the present disclosure, the second
plurality of ionic particles include ammonium acetate.
Under another aspect of the present disclosure, the second
plurality of ionic particles include ammonium carbonate.
Under another aspect of the present disclosure, the second
plurality of ionic particles include ammonium bicarbonate. ionic
organic species, and ionic polymers
Under another aspect of the present disclosure, the second
plurality of ionic particles include ionic organic species.
Under another aspect of the present disclosure, the second
plurality of ionic particles include ionic polymers.
Under another aspect of the present disclosure, the second
plurality of ionic particles include inorganic salts.
Under another aspect of the present disclosure, the liquid medium
is an aqueous solution.
Under another aspect of the present disclosure, the liquid medium
is a nitric acid solution.
Under another aspect of the present disclosure, the liquid medium
is a sulfuric acid solution.
Under another aspect of the present disclosure, the concentration
level of nanotube elements within the nanotube application solution
is increased in order to promote rafting in a nanotube fabric layer
formed with such a solution.
Under another aspect of the present disclosure, the concentration
level of nanotube elements within the nanotube application solution
is decreased in order to discourage rafting in a nanotube fabric
layer formed with such a solution.
Under another aspect of the present disclosure, the concentration
level of ionic particles within the nanotube application solution
is decreased in order to promote rafting in a nanotube fabric layer
formed with such a solution.
Under another aspect of the present disclosure, the concentration
level of ionic particles within the nanotube application solution
is increased in order to discourage rafting in a nanotube fabric
layer formed with such a solution.
Other features and advantages of the present invention will become
apparent from the following description of the invention which is
provided below in relation to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration depicting a nanotube fabric layer
exhibiting essentially no rafting of the individual nanotube
elements;
FIGS. 2A-2B are SEM images (at different magnifications) of a
nanotube fabric layer exhibiting essentially no rafting of the
individual nanotube elements;
FIG. 3 is an illustration depicting a nanotube fabric layer
exhibiting substantial rafting of the individual nanotube elements,
according to one or more embodiments of the present disclosure;
FIGS. 4A-4B are SEM images (at different magnifications) of a
nanotube fabric layer exhibiting substantial rafting of the
individual nanotube elements, according to one or more embodiments
of the present disclosure;
FIG. 5 is a process diagram illustrating a method according to the
present disclosure of preparing a nanotube application solution
such as to form a highly rafted nanotube fabric layer;
FIG. 6 is a process diagram illustrating a method according to the
present disclosure of preparing a nanotube application solution
such as to form a substantially non-rafted nanotube fabric
layer;
FIG. 7 is a graph plotting conductivity readings (measured in
.mu.S/cm) vs. ammonium nitrate salt levels (measure in ppm) taken
on a plurality of nanotube application solutions;
FIGS. 8A-8C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 11.6%
rafting;
FIGS. 9A-9C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 18.9%
rafting;
FIGS. 10A-10C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 5.5%
rafting;
FIGS. 11A-11C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 37.8%
rafting;
FIGS. 12A-12C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits substantially no rafting;
FIGS. 13A-13C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits substantially no rafting;
FIGS. 14A-14C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 13.1%
rafting;
FIGS. 15A-15C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 10.0%
rafting;
FIGS. 16A-16C are SEM images (at increasing magnifications) of an
exemplary nanotube fabric layer formed according to the methods of
the present disclosure which exhibits approximately 35.0%
rafting;
FIG. 17A is a diagram illustrating three steps within a nanotube
deposition process using a nanotube formulation with a relatively
high ionic species concentration level;
FIG. 17B is a diagram illustrating three steps within a nanotube
deposition process using a nanotube formulation with a relatively
low ionic species concentration level;
FIG. 18A is an TEM image of a cross-section of a nanotube fabric
with a relatively high surface roughness;
FIG. 18B is a line drawing of the TEM image of FIG. 18A;
FIG. 19A is an TEM image of a cross-section of a nanotube fabric
with a relatively low surface roughness;
FIG. 19B is a line drawing of the TEM image of FIG. 19A;
FIGS. 20A and 20B are first and second TEM images, respectively, of
a first exemplary type of nanotube;
FIGS. 20C and 20D are first and second TEM images, respectively, of
a second exemplary type of nanotube;
FIGS. 20E and 20F are first and second TEM images, respectively, of
a third exemplary type of nanotube;
FIG. 21 is a table of cations and anions which can be used to form
a plurality of ionic species well-suited for use with the methods
of the present disclosure;
FIG. 22 is a labeled example of a nanotube formulation roughness
curve;
FIG. 23A is a flow chart detailing a method for producing a carbon
nanotube (CNT) fabric with a preselected surface roughness and
degree of rafting according to the methods of the present
disclosure;
FIG. 23B is a flow chart depicting a first exemplary ionic species
adjustment process according to the methods of the present
disclosure, which is imagined to be designed to reduce the ionic
species concentration level of a CNT formulation to a very low or
substantially zero value;
FIG. 23C is a flow chart depicting a second exemplary ionic species
adjustment process according to the methods of the present
disclosure, which is imagined to be designed to substantially
remove a first type of ionic species from a CNT formulation and
replace it with a second type of ionic species at a selected
concentration level;
FIG. 23D is a flow chart depicting a third exemplary Ionic Species
Adjustment Process according to the methods of the present
disclosure, which is imagined to be designed to first exchange an
undesired first type of ionic species within a CNT Formulation with
a desired second type of ionic species and then lower the
concentration level of that second type of ionic species within the
formulation to a desired target level;
FIG. 24 is a flow chart detailing a method according to the present
disclosure for generating a nanotube formulation roughness curve
for a particular nanotube formulation with a selected ionic
species;
FIG. 25 is a table summarizing the data and results presented in
examples 10-23;
FIG. 26A is a nanotube formulation roughness curve according to the
methods of the present disclosure corresponding to nanotube
formulation "B" (as defined within the present disclosure) used
with ammonium nitrate (NH.sub.4NO.sub.3) as an ionic species;
FIG. 26B is a nanotube formulation roughness curve according to the
methods of the present disclosure corresponding to nanotube
formulation "B" (as defined within the present disclosure) used
with tetramethyl ammonium formate (TMA Fm) as an ionic species;
FIG. 26C is a nanotube formulation roughness curve according to the
methods of the present disclosure corresponding to nanotube
formulation "C" (as defined within the present disclosure) used
with ammonium nitrate (NH.sub.4NO.sub.3) as an ionic species;
FIG. 26D is a nanotube formulation roughness curve according to the
methods of the present disclosure corresponding to nanotube
formulation "C" (as defined within the present disclosure) used
with tetramethyl ammonium formate (TMA Fm) as an ionic species;
FIG. 27 is a diagram illustrating a material layer height mapping
method used to illustrate the surface roughness of nanotube fabrics
formed within examples 10-23;
FIG. 28A is an SEM image illustrating the resulting nanotube fabric
within example 10 of the present disclosure;
FIG. 28B is a topographical plot of the surface of the resulting
nanotube fabric within example 10 of the present disclosure;
FIG. 28C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 10 of the present disclosure;
FIG. 29A is an SEM image illustrating the resulting nanotube fabric
within example 11 of the present disclosure;
FIG. 29B is a topographical plot of the surface of the resulting
nanotube fabric within example 11 of the present disclosure;
FIG. 29C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 11 of the present disclosure;
FIG. 30A is an SEM image illustrating the resulting nanotube fabric
within example 12 of the present disclosure;
FIG. 30B is a topographical plot of the surface of the resulting
nanotube fabric within example 12 of the present disclosure;
FIG. 30C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 12 of the present disclosure;
FIG. 31A is an SEM image illustrating the resulting nanotube fabric
within example 13 of the present disclosure;
FIG. 31B is a topographical plot of the surface of the resulting
nanotube fabric within example 13 of the present disclosure;
FIG. 31C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 13 of the present disclosure;
FIG. 32A is an SEM image illustrating the resulting nanotube fabric
within example 14 of the present disclosure;
FIG. 32B is a topographical plot of the surface of the resulting
nanotube fabric within example 14 of the present disclosure;
FIG. 32C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 14 of the present disclosure;
FIG. 33A is an SEM image illustrating the resulting nanotube fabric
within example 15 of the present disclosure;
FIG. 33B is a topographical plot of the surface of the resulting
nanotube fabric within example 15 of the present disclosure;
FIG. 33C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 15 of the present disclosure;
FIG. 34A is an SEM image illustrating the resulting nanotube fabric
within example 16 of the present disclosure;
FIG. 34B is a topographical plot of the surface of the resulting
nanotube fabric within example 16 of the present disclosure;
FIG. 34C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 16 of the present disclosure;
FIG. 35A is an SEM image illustrating the resulting nanotube fabric
within example 17 of the present disclosure;
FIG. 35B is a topographical plot of the surface of the resulting
nanotube fabric within example 17 of the present disclosure;
FIG. 35C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 17 of the present disclosure;
FIG. 36A is an SEM image illustrating the resulting nanotube fabric
within example 18 of the present disclosure;
FIG. 36B is a topographical plot of the surface of the resulting
nanotube fabric within example 18 of the present disclosure;
FIG. 36C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 18 of the present disclosure;
FIG. 37A is an SEM image illustrating the resulting nanotube fabric
within example 19 of the present disclosure;
FIG. 37B is a topographical plot of the surface of the resulting
nanotube fabric within example 19 of the present disclosure;
FIG. 37C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 19 of the present disclosure;
FIG. 38A is an SEM image illustrating the resulting nanotube fabric
within example 20 of the present disclosure;
FIG. 38B is a topographical plot of the surface of the resulting
nanotube fabric within example 20 of the present disclosure;
FIG. 38C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 20 of the present disclosure;
FIG. 39A is an SEM image illustrating the resulting nanotube fabric
within example 21 of the present disclosure;
FIG. 39B is a topographical plot of the surface of the resulting
nanotube fabric within example 21 of the present disclosure;
FIG. 39C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 21 of the present disclosure;
FIG. 40A is an SEM image illustrating the resulting nanotube fabric
within example 22 of the present disclosure;
FIG. 40B is a topographical plot of the surface of the resulting
nanotube fabric within example 22 of the present disclosure;
FIG. 40C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 22 of the present disclosure;
FIG. 41A is an SEM image illustrating the resulting nanotube fabric
within example 23 of the present disclosure;
FIG. 41B is a topographical plot of the surface of the resulting
nanotube fabric within example 23 of the present disclosure;
FIG. 41C is a normalized histogram plotting the positional
orientation frequency of the nanotube elements within the resulting
nanotube fabric within example 23 of the present disclosure.
DETAILED DESCRIPTION
The present disclosure teaches methods to increase or reduce the
number of nanotube elements in a given area of nanotube fabric
layers and films. These approaches can selectively create high
density, low porosity nanotube fabrics in a controlled way. In this
manner, for example, nanotube fabrics may be created in which
essentially all gaps or pores between nanotubes within the fabric
are no larger than a predetermined size. This is particularly
useful for devices with extremely small circuit sizes in which a
uniform dispersion of nanotubes is desired. For example, when a
fabric with a high density and low porosity is patterned and
etched, the remaining nanotube article is effectively assured of
containing nanotubes as opposed to lacking nanotubes as a result of
a large pore in the fabric. As the feature sizes decrease along
with currently practiced lithography techniques, minimizing the
porosity becomes more important to ensure a higher yield of
functional circuit elements as the fabric is being etched. For
example, the high density, low porosity fabrics can have nanotube
free regions, i.e., pores that are less than the size of the small
circuits according to the current lithography techniques (e.g.,
pores that are less than about 10 nm). Thus, the density or pore
size is controlled such that the minimum number of nanotube
elements required for operation can be utilized in a critical
feature size of current lithography techniques, (e.g. 20 nm or
less) which can be less than 20 nm.
Conversely, the methods can be used to create highly porous, low
density fabrics, if so desired. For example, it may desirable to
have a nanotube fabric where the nanotubes are dispersed to
increase the optical transparency of the nanofabric. In other
applications, where a thicker fabric, formed of multiple layers of
nanotube fabrics, is desired, it may be preferable to limit the
concentration of nanotubes to reduce cost and the electrical
resistance of the fabric. Further, for low density and high
porosity fabrics, it is also important that the nanotubes be
dispersed in a uniform manner across the fabric.
Fabric porosity and density may be controlled in a variety of ways
including, but not limited to, techniques for controlling rafting
within the nanotube fabric. These fabrics can then be used in
nanotube switching devices.
As described within U.S. Pat. No. 7,375,369 to Sen et al. and U.S.
patent application Ser. No. 11/304,315 to Ghenciu et al., both
incorporated herein by reference in their entirety, nanotube
fabrics and films can be formed by applying a nanotube application
solution (for example, but not limited to, a plurality of
individual nanotube elements suspended within an aqueous solution)
over a substrate element. A spin coating process, for example, can
be used to evenly distribute the nanotube elements over the
substrate element, creating a substantially uniform layer of
nanotube elements. In other cases, other processes (such as, but
not limited to, spray coating processes or dip coating processes)
can be used to apply and distribute the nanotube elements over the
substrate element.
It should be noted that nanotube elements used and referenced
within the embodiments of the present disclosure may be single
walled nanotubes, multi-walled nanotubes, or mixtures thereof and
may be of varying lengths. Further, the nanotubes may be
conductive, semiconductive, or combinations thereof.
Within many applications it is desirable to control the porosity of
a nanotube fabric layer as it is formed--that is, to control how
closely packed together or sparsely distributed the individual
nanotube elements within the fabric layer are. In one example, a
high porosity uniform nanotube fabric may have voids--that is gaps
in the fabric between individual nanotube elements--on the order of
50 nm in size. In another example, a low porosity uniform nanotube
fabric layer may have voids on the order of 10 nm in size.
In some applications the sheet resistance of a nanotube fabric
layer may be controlled by controlling the porosity of the nanotube
fabric layer, or a density of nanotubes in the fabric, along with
other variables (such as, but not limited to, the length of the
individual nanotube elements within the fabric and the thickness of
the nanotube fabric layer). By controlling the porosity of a
nanotube fabric layer, such a fabric layer can be reliably tuned to
have a sheet resistance from about 1 k-Ohm/square to about 1
M-Ohm/square.
In another applications by limiting the porosity of a nanotube
fabric layer the density of an array of nanotube switching devices
may be increased. U.S. patent application Ser. No. 11/280,786 to
Bertin et al., incorporated herein by reference in its entirety,
teaches a nonvolatile two terminal nanotube switch structure having
(in at least one embodiment) a nanotube fabric article deposited
between two electrically isolated electrode elements. As Bertin
teaches, by placing different voltages across said electrode
elements, the resistive state of the nanotube fabric article can be
switched between a plurality of nonvolatile states. That is, in
some embodiments the nanotube fabric article can be repeatedly
switched between a relatively high resistive state (resulting in,
essentially, an open circuit between the two electrode elements)
and a relatively low resistive state (resulting in, essentially, a
short circuit between the two electrode elements).
The fabrication of an array of such nanotube switching devices can
include patterning of a nanotube fabric layer to realize a
plurality of these nanotube fabric articles. The porosity of a
nanotube fabric layer--or more specifically the size of the voids
within a nanotube fabric layer--can limit the feature size to which
these nanotube fabric articles can be patterned. For example, to
fabricate a nanotube switching device array wherein the individual
nanotube switching devices are on the order of 20 nm square (that
is, the nanotube fabric article within each device is essentially
20 nm by 20 nm), the porosity of the nanotube fabric array may need
to be such that voids within the nanotube fabric layer are on the
order of 10 nm. In this way, the fabrication of highly dense
nanotube memory arrays (wherein the individual nanotube switching
elements within the array are patterned at a sub 20 nm geometry,
for example) can require highly dense (that is, less porous with
void sizes on the order of 10 nm or less) nanotube fabric
layers.
One method of controlling the porosity of a nanotube fabric layer
is to control the degree of rafting--that is, the percentage of
nanotube elements within the fabric layer which tend to bundle
together along their sidewalls--within the nanotube fabric layer.
By controlling certain parameters during the formation of a
nanotube fabric layer, a nanotube fabric layer can be formed which
is highly rafted (and, consequently, highly dense--for example,
with voids on the order of 10 nm), moderately rafted (and,
consequently, marginally dense--for example, with voids on the
order of 25 nm), or substantially free from rafts (and
consequently, highly porous--for example with voids on the order of
50 nm).
FIG. 1 depicts a nanotube fabric layer 100 which is substantially
free of rafts. As described above, within such a fabric layer
individual nanotube elements 110 are formed into a uniform highly
porous fabric wherein the individual nanotube elements are arranged
in substantially random orientations. For example, the voids within
such a fabric layer 100 might range between 25 nm and 50 nm,
corresponding to a sheet resistance between about 1000 k-Ohm/square
to 1 M-Ohm/square within a single fabric layer. A thicker fabric
layer may be formed with substantially the same porosity by
applying (through multiple spin coating operations, for example)
multiple fabric layers over the nanotube fabric layer 100
illustrated in FIG. 1.
FIGS. 2A and 2B are SEM images depicting an exemplary nanotube
fabric layer (201 and 202, respectively) substantially free of
rafts and analogous to the nanotube fabric layer 100 depicted in
FIG. 1. FIG. 2A shows the nanotube fabric layer 201 at a
10,000.times. magnification, and FIG. 2B shows the nanotube fabric
layer 202 at a 75,000.times. magnification. Within both images, the
random orientation--and essentially complete lack of rafting--is
evident within the exemplary nanotube fabric layer.
FIG. 3 depicts a nanotube fabric layer 300 which includes a
moderate number of rafted nanotube bundles 320 as well as a number
of unbundled nanotube elements 310. Within such a fabric layer,
individual nanotube elements within the rafted bundles 320 are
packed tightly together such as to minimize the porosity within
that region of the nanotube fabric layer 300. In this way, the
nanotube fabric layer 300 is significantly denser as compared to
the fabric layer 100 illustrated in FIG. 1. For example, the voids
within such a fabric layer 300 might range between 10 nm and 20 nm,
corresponding to a sheet resistance between about 10 k-Ohm/square
to 100 k-Ohm/square within a single fabric layer. A thicker fabric
layer may be formed with substantially the same porosity by
applying (through multiple spin coating operations, for example)
multiple fabric layers over the nanotube fabric layer 300
illustrated in FIG. 3.
FIGS. 4A and 4B are SEM images depicting an exemplary nanotube
fabric layer (401 and 402, respectively) which exhibits a moderate
amount of rafting and is analogous to the nanotube fabric layer 300
depicted in FIG. 3. FIG. 4A shows the nanotube fabric layer 401 at
a 10,000.times. magnification, and FIG. 4B shows the nanotube
fabric layer 402 at a 75,000.times. magnification. Within both
images, the randomly oriented bundles of rafted nanotube elements
(410 and 420, respectively) are evident within the exemplary
nanotube fabric layer.
In some cases, rafting of individual nanotube elements can occur
because during the formation of a nanotube fabric layer groups of
nanotube elements bundle together along their sidewalls due to van
der Waals interactions (atomic level forces between the individual
nanotube elements) or through JI-JI interactions (a stacking effect
due to the presence of a free electrons in the JI-orbitals along
the nanotube structure). Within an application solution--that is, a
dispersion of individual nanotube elements within a liquid
medium--the van der Waals and JI-JI interactions can be promoted or
discouraged by the presence of certain ionic species within the
solution. Such ionic species include, but are not limited to,
ammonium salts, nitrate salts, ammonium nitrate salts, ammonium
formate, ammonium acetate, ammonium carbonate, ammonium
bicarbonate, ionic organic species, ionic polymers, and inorganic
salts. A high concentration of such ionic species within the
application solution (for example, on the order of 20 ppm or more
ammonium nitrate salts within an aqueous nanotube application
solution) will tend to interfere with these interactions and
thereby reduce the degree of rafting within a nanotube fabric layer
formed with such an application solution. Conversely, a low
concentration of such ionic species within the application solution
(for example, on the order of 10 ppm or less ammonium nitrate salts
within an aqueous nanotube application solution) will tend to allow
a plurality of these rafted bundles to form within a nanotube
fabric layer.
It should be noted that this rafting effect--wherein a plurality of
nanotube elements bundle together along their sidewalls to realize
an orderly raft like structure--is different from the so-called
clumping defects described within U.S. patent application Ser. No.
11/304,315 to Ghenciu et al., the entire disclosure of which is
hereby incorporated by reference. The clumping defects described by
Ghenciu are the result of precipitation or aggregation of the
individual nanotube elements within the solution and are
characterized by individual nanotube elements twisting around each
other and bundling into clump like structures within the
application solution. Such undesirable clumping defects can result
in non-uniform and non-planar nanotube fabric layers. Conversely,
as described by the present disclosure, a rafted nanotube fabric
can remain, in most cases, substantially uniform and thus can be
employed to control the density of a nanotube fabric layer.
Further, the rafts described herein are essentially two dimensional
nanotube structures, i.e., the height of the raft is generally one
nanotube thick. The clumping defects referenced in Ghenciu
generally result in three dimensional nanotube clumps.
Rafting also can be promoted (or discouraged) by controlling the
concentration of nanotube elements with an application
solution--that is, by controlling the number of individual nanotube
elements per unit volume present within the applicator liquid. Van
der Waals interactions between closely situated nanotube elements
within a highly concentrated application solution (for example, an
application solution with an optical density on the order of 35)
can tend to increase the incidence of rafting within a nanotube
fabric layer formed with such a solution. Conversely, an
application solution with a relatively low concentration of
nanotube elements (for example, an application solution with an
optical density on the order of 10) can significantly reduce the
opportunity for these van der Waals interactions and result in less
rafting. It should be noted that optical density (a spectrographic
technique well known to those skilled in the art) is typically used
to characterize the density of nanotube elements within an
application solution. The technique relies on measuring the amount
of light absorbed by a nanotube application solution--essentially
the light absorbed by the individual nanotube elements within such
a solution--to determine the concentration of nanotube elements
dispersed in the solution. For example, a solution with an optical
density of 30 corresponds to approximately 0.1% concentration (by
weight) of nanotube elements within the solution.
The use of these two parameters (the concentration of an ionic
species within the application solution and nanotube concentration
within the application solution) to control the degree of rafting
within a nanotube fabric layer is illustrated in the exemplary
nanotube fabric layers depicted in FIGS. 7A-7C, 8A-8C, 9A-9C,
10A-10C, and 11A-11C and described in detail within the discussion
of those figures.
In addition, within certain applications other parameters of a
nanotube application solution may contribute to the degree to which
a nanotube fabric layer formed with that solution will raft. Such
parameters include, but are not limited to, the presence of other
carbon allotropes (for example, amorphous carbon), the temperature
of the application solution as it is applied to the surface of a
wafer or other substrate, the chemical composition of the liquid
medium used, the method used for depositing the application
solution to the surface of a wafer or other substrate, and the
acidity of the solution.
FIG. 5 illustrates an exemplary application solution preparation
process according to the methods of the present disclosure which is
well suited for forming a rafted nanotube fabric layer.
At the start of the application solution preparation process
illustrated in FIG. 5, a plurality of individual nanotube elements
505 is dispersed into a liquid medium 510 (such as, but not limited
to, an aqueous solution, a sulfuric acid solution, or a nitric acid
solution) to form raw nanotube application solution 515. Raw
nanotube application solution 515 includes a plurality of
individual nanotube elements 560, a plurality of impurities (such
as, but not limited to, residual metallic catalyst particles,
amorphous carbon particles, and other carbonaceous impurities) 565,
and a concentration of an ionic particles 570 (such as, but not
limited to, ammonium salts, nitrate salts, ammonium nitrate salts,
ammonium formate, ammonium acetate, ammonium carbonate, ammonium
bicarbonate, ionic organic species, ionic polymers, and inorganic
salts). The raw nanotube application solution 515 is then passed
through a filtration/purification process 520 which removes a
significant percentage of impurities 565 to realize purified
nanotube application solution 525. A typical
filtration/purification process 520 also can remove a percentage of
the ionic particles 570 within raw nanotube application solution
515, as is shown in the graphic representation of the purified
nanotube application solution 525 in FIG. 5.
A typical purified nanotube application solution 525 can include
less than 1.times.10.sup.18 atoms/cm.sup.3 of impurities 565 and be
substantially free of particle impurities 565 having a diameter of
greater than about 500 nm. It also can include a nanotube
concentration of 100 mg/l (a nanotube concentration well suited for
memory and logic applications). This typical purified nanotube
application solution 525 might also include an ionic species of
ammonium nitrate salt at a concentration of about 15 ppm.
The formation and purification of nanotube application solutions
(such as described above) is taught in U.S. Pat. No. 7,375,369 to
Sen et al. as well as U.S. patent application Ser. No. 11/304,315
to Ghenciu et al. Within both references, a plurality of
filtration/purification processes are detailed, including cross
flow filtration, nitric acid treatment, hydrochloric acid
treatment, and high speed centrifugation.
Within the exemplary process detailed in FIG. 5, the purified
nanotube application solution 525 is then passed through an ionic
particle concentration level adjustment process 530 which further
reduces the concentration of ionic particles 570 within the
purified application solution 530 resulting in intermediate
application solution 535. For an exemplary ionic species of
ammonium nitrate salts, this intermediate application solution 535
can have an ionic particle concentration level of less than 10 ppm.
This ionic particle concentration level adjustment process 530 may
be realized through an additional filtering process (such as, but
not limited to, a cross flow filtration process, a sonication
filtration process, and a centrifugation filtration process).
In a next process step, intermediate application solution 535 is
passed through a nanotube concentration adjustment process 540,
which increases the concentration of nanotube elements within the
intermediate application solution 535 resulting in a final
application solution 545, which is well suited for forming a rafted
nanotube fabric layer. For example, the nanotube application
solution can be adjusted such that final application solution 545
possesses an optical density on the order of 35. Typically such a
nanotube concentration adjustment process 540 is realized by
removing a volume of the liquid medium 510 from the solution,
though the methods of the present disclosure are not limited in
this regard.
Within the exemplary process detailed in FIG. 5, a spin coating
process 550 is used to apply final nanotube application solution
545 over a silicon wafer to realize rafted nanotube fabric layer
555 wherein a plurality of rafted bundles of nanotube elements 575
are distributed throughout the fabric layer.
In this way a purified nanotube application solution 525 (prepared
according to the methods taught by Sen and Ghenciu) is rendered
into an application solution 545 well suited for forming a rafted
nanotube fabric layer by reducing the concentration of ionic
particles within the original purified solution in one operation
and by increasing the concentration of nanotube elements within the
solution in a second operation.
It should be noted that while the exemplary process detailed in
FIG. 5 describes a specific nanotube application solution process
in order to illustrate the methods of the present disclosure, the
methods of the present disclosure are not limited to this specific
example. For example, within some applications the order of the
ionic particle concentration level adjustment process 530 and the
nanotube concentration adjustment process 540 can be reversed (that
is, the application solution first increased in nanotube
concentration and then reduced in ionic particle concentration).
Further, within some applications the ionic particle concentration
level adjustment process 530 may be removed altogether and the
nanotube concentration adjustment process 540 used alone to
sufficiently render purified nanotube application solution 525 into
a solution well suited for forming a rafted nanotube fabric layer.
Within still other applications, the nanotube concentration
adjustment process 540 may be removed altogether and the ionic
particle concentration level adjustment process used alone to
sufficiently render purified nanotube application solution 525 into
a solution well suited for forming a rafted nanotube fabric
layer.
FIG. 6 illustrates an exemplary application solution preparation
process according to the methods of the present disclosure which is
well suited for forming a nanotube fabric layer substantially free
of rafted bundles of nanotube elements.
At the start of the application solution preparation process
illustrated in FIG. 6, a plurality of individual nanotube elements
605 is dispersed into a liquid medium 610 (such as, but not limited
to an aqueous solution, a sulfuric acid solution, or a nitric acid
solution) to form raw nanotube application solution 615. Raw
nanotube application solution 615 includes a plurality of
individual nanotube elements 660, a plurality of impurities (such
as, but not limited to, residual metallic catalyst particles,
amorphous carbon particles, and other carbonaceous impurities) 665,
and a concentration of ionic particles 670 (such as, but not
limited to, ammonium salts, nitrate salts, ammonium nitrate salts,
ammonium formate, ammonium acetate, ammonium carbonate, ammonium
bicarbonate, ionic organic species, ionic polymers, and inorganic
salts). The raw nanotube application solution 615 is then passed
through a filtration/purification process 620 which removes a
significant percentage of impurities 665 to realize purified
nanotube application solution 625. A typical
filtration/purification process 620 can remove a percentage of the
ionic particles 670 within raw nanotube application solution 615,
as is shown in the graphic representation of the purified nanotube
application solution 625 in FIG. 6.
A typical purified nanotube application solution 625 can include
less than 1.times.10.sup.18 atoms/cm.sup.3 of impurities 665 and be
substantially free of particle impurities 665 having a diameter of
greater than about 500 nm. It also can have a nanotube
concentration of 100 mg/l (a nanotube concentration well suited for
memory and logic applications). This typical purified nanotube
application solution 625 also can include an ionic species of
ammonium nitrate salt at a concentration of about 15 ppm.
The formation and purification of nanotube application solutions
(such as described above) is taught in U.S. Pat. No. 7,375,369 to
Sen et al. as well as U.S. patent application Ser. No. 11/304,315
to Ghenciu et al. Within both references, a plurality of
filtration/purification processes are detailed, including cross
flow filtration, nitric acid treatment, hydrochloric acid
treatment, and high speed centrifugation.
Within the exemplary process detailed in FIG. 6, the purified
nanotube application solution 625 is then passed through an ionic
particle concentration level adjustment process 630 which increases
the concentration of ionic particles 670 within the purified
application solution 625 resulting in intermediate application
solution 635. For an exemplary ionic species of ammonium nitrate
salts, this intermediate application solution 535 can include an
ionic particle concentration level of greater than 30 ppm. This
ionic particle concentration level adjustment process 625 can be
realized through the introduction of an additional quantity of
ionic particles 670 into the purified application solution 625.
In a next process step, intermediate application solution 635 is
passed through a nanotube concentration adjustment process 640,
which decreases the concentration of nanotube elements within
intermediate application solution 635 resulting in a final
application solution 645, which is well suited for forming a
nanotube fabric layer substantially free of rafted bundles of
nanotube elements. For example the nanotube application solution
can be adjusted such that final application solution 645 possesses
an optical density on the order of 10. Typically, such a nanotube
concentration adjustment process 640 can be realized by adding an
additional volume of the liquid medium 610 into the solution,
though the methods of the present disclosure are not limited in
this regard.
Within the exemplary process detailed in FIG. 6, a spin coating
process 650 is used to apply final nanotube application solution
645 over a silicon wafer to realize nanotube fabric layer 655 which
is substantially free of rafted bundles of nanotube elements.
In this way a purified nanotube application solution 625 (prepared
according to the methods taught by Sen and Ghenciu) is rendered
into an application solution 645 well suited for forming a nanotube
fabric layer substantially free of rafted bundles of nanotube
elements by increasing the concentration of ionic particles within
the original purified solution in one operation and by decreasing
the concentration of nanotube elements within the solution in a
second operation.
It should be noted that while the exemplary process detailed in
FIG. 6 describes a specific nanotube application solution process
in order to illustrate the methods of the present invention, the
methods of the present invention are not limited to this specific
example. Indeed, within some applications the order of the ionic
particle concentration level adjustment process 630 and the
nanotube concentration adjustment process 640 can be reversed (that
is the application solution first decreased in nanotube
concentration and then increased in ionic particle concentration).
Further, within some applications the ionic particle concentration
level adjustment process 630 may be removed altogether and the
nanotube concentration adjustment process 640 used alone to
sufficiently render purified nanotube application solution 625 into
a solution well suited for forming a nanotube fabric layer
substantially free from rafted bundles of nanotube elements. Within
still other applications, the nanotube concentration adjustment
process 640 may be removed altogether and the ionic particle
concentration level adjustment process used alone to sufficiently
render purified nanotube application solution 625 into a solution
well suited for forming a nanotube fabric layer substantially free
from rafted bundles of nanotube elements.
The following examples describe the formation of several nanotube
fabric layers (with varying degrees of rafting) according to the
methods of the present disclosure. Within each example, a purified
nanotube application solution was first realized through the
methods taught by Ghenciu in U.S. patent application Ser. No.
11/304,315 (and described in the discussions of FIGS. 5 and 6).
This purified nanotube application solution was then adjusted as
specified in each example to realize a specific nanotube
concentration and ionic particle concentration level. Within each
example the ionic species adjusted was ammonium nitrate salts. The
resulting solution was then deposited on a four inch Si/SiO.sub.2
wafer via a spin coating operation. For all examples, the nanotube
concentration is measured in terms of optical density (a
spectrographic technique well known to those skilled in the art),
and the ammonium nitrate salt concentration is measured in
parts-per-million (ppm) with respect to the solution.
It should be noted that while the following examples specify the
level of ammonium nitrate salt (the exemplary ionic species used in
each of the examples) in terms of ppm, another methods of tracking
an ionic species concentration level may prove more convenient for
some applications. FIG. 7 is a graph plotting the conductivity
(measured in .mu.S/cm) of a plurality of nanotube application
solutions against the concentration level (measured in ppm) of
ammonium nitrate salts in each application solution. As can be
observed in FIG. 7, the conductivity of these application solutions
will tend to track the concentration of ammonium nitrate salts
dispersed in each. For example, within the application solutions
used in the following example, a conductivity reading of
approximately 700 .mu.S/cm or higher would indicate that an
application solution would be likely to promote rafting.
Conversely, a conductivity reading of approximately 500 .mu.S/cm or
lower would indicate that an application solution would be likely
to discourage rafting. As such, it may be convenient within some
applications of the methods of the present disclosure to track and
adjust the conductivity of a nanotube application solution instead
of the concentration level of a particular ionic species within
that application solution.
For all examples, the spin coating operation was as follows. A raw
wafer was pre-baked on a 300.degree. C. hot plate for five minutes.
Approximately 3 ml of the adjusted solution was dispensed onto the
wafer via a plastic pipette while the wafer was rotated at 60 rpm.
After thirty seconds, the spin speed was increased to 500 rpm for
two seconds, then subsequently reduced to fifty rpm for 180
seconds, and finally increased to 2000 rpm for twenty seconds. The
wafer (now coated with the application solution) was then placed on
a 300.degree. C. hot plate for two minutes. After a cool down
cycle, the entire process was repeated again twice such as to apply
three coats of the application solution over the wafer.
For the application solutions used in the following examples it was
found that generally an ammonium nitrate salt concentration level
of 10 ppm or lower would tend to result in a highly rafted fabric.
It was further found that generally an ammonium nitrate salt
concentration level of 20 ppm or more would tend to result in
fabric layers with lower incidences of rafting. Applications
solutions with ammonium nitrate salt concentration levels between
these ranges were found to result in fabric layers with moderate
rafting.
Further, for the application solutions used in the following
examples it was found that generally an optical density of
approximately 10 or lower would tend to result in fabric layers
with low incidences of rafting. It was further found that generally
an optical density of 30 or more would tend to result in fabric
layers with very high incidences of rafting. Applications solutions
with optical densities between these ranges were found to result in
fabric layers with moderate rafting.
Example 1
FIGS. 8A-8C are SEM images of an exemplary nanotube fabric layer at
different magnifications (801, 802, and 803 respectively) prepared
according to the methods of the present disclosure. The nanotube
fabric layer depicted in FIGS. 8A-8C was rendered from an
application solution with an optical density of 19.11 and an
ammonium nitrate salt concentration of 16 ppm. These parameters
resulted in a moderate amount of rafting within the nanotube fabric
layer (801, 802, 803). Analysis of the entire nanotube fabric layer
showed that approximately 11.6% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 8A (810), FIG. 8B
(820), and FIG. 8C (830).
Example 2
FIGS. 9A-9C are SEM images of an exemplary nanotube fabric layer at
different magnifications (901, 902, and 903 respectively) prepared
according to the methods of the present disclosure. The nanotube
fabric layer depicted in FIGS. 9A-9C was rendered from an
application solution with an optical density of 34.35 and an
ammonium nitrate salt concentration of 12 ppm. These parameters
resulted in a high degree of rafting within the nanotube fabric
layer (901, 902, 903). Analysis of the entire nanotube fabric layer
showed that approximately 18.9% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 9A (910), FIG. 9B
(920), and FIG. 9C (930).
Example 3
FIGS. 10A-10C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1001, 1002, and 1003 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 10A-10C was rendered from
an application solution with an optical density of 10.02 and an
ammonium nitrate salt concentration of 11 ppm. These parameters
resulted in a low degree of rafting within the nanotube fabric
layer (1001, 1002, 1003). Analysis of the entire nanotube fabric
layer showed that approximately 5.5% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 10A (1010), FIG.
10B (1020), and FIG. 10C (1030).
Example 4
FIGS. 11A-11C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1101, 1102, and 1103 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 11A-11C was rendered from
an application solution with an optical density of 19.69 and an
ammonium nitrate salt concentration of 1.5 ppm. These parameters
resulted in a high degree of rafting within the nanotube fabric
layer (1101, 1102, 1103). Analysis of the entire nanotube fabric
layer showed that approximately 37.8% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 11A (1110), FIG.
11B (1120), and FIG. 11C (1130).
Example 5
FIGS. 12A-12C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1201, 1202, and 1203 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 12A-12C was rendered from
an application solution with an optical density of 19.71 and an
ammonium nitrate salt concentration of 25 ppm. These parameters
resulted in substantially no rafting within the nanotube fabric
layer (1201, 1202, 1203). Analysis of the entire nanotube fabric
layer showed that the fabric layer was substantially free of rafted
bundles of nanotube elements.
Example 6
FIGS. 13A-13C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1301, 1302, and 1303 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 13A-13C was rendered from
an application solution with an optical density of 10.02 and an
ammonium nitrate salt concentration of 27 ppm. These parameters
resulted in substantially no rafting within the nanotube fabric
layer (1301, 1302, 1303). Analysis of the entire nanotube fabric
layer showed that the fabric layer was substantially free of rafted
bundles of nanotube elements.
Example 7
FIGS. 14A-14C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1401, 1402, and 1403 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 14A-14C was rendered from
an application solution with an optical density of 9.4 and an
ammonium nitrate salt concentration of 2.5 ppm. These parameters
resulted in a moderate degree of rafting within the nanotube fabric
layer (1401, 1402, 1403). Analysis of the entire nanotube fabric
layer showed that approximately 13.1% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 14A (1410), FIG.
14B (1420), and FIG. 14C (1430).
Example 8
FIGS. 15A-15C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1501, 1502, and 1503 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 15A-15C was rendered from
an application solution with an optical density of 33.9 and an
ammonium nitrate salt concentration of 33 ppm. These parameters
resulted in a moderate degree of rafting within the nanotube fabric
layer (1501, 1502, 1503). Analysis of the entire nanotube fabric
layer showed that approximately 10.0% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 15A (1510), FIG.
15B (1520), and FIG. 15C (1530).
Example 9
FIGS. 16A-16C are SEM images of an exemplary nanotube fabric layer
at different magnifications (1601, 1602, and 1603 respectively)
prepared according to the methods of the present disclosure. The
nanotube fabric layer depicted in FIGS. 16A-16C was rendered from
an application solution with an optical density of 33.9 and an
ammonium nitrate salt concentration of 7.5 ppm. These parameters
resulted in a high degree of rafting within the nanotube fabric
layer (1601, 1602, 1603). Analysis of the entire nanotube fabric
layer showed that approximately 35.0% of the fabric (by area) was
comprised of rafted bundles of nanotube elements. These rafted
bundles of nanotube elements are evident in FIG. 16A (1610), FIG.
16B (1620), and FIG. 16C (1630).
We have described multiple techniques to control the porosity
and/or density of a nanotube fabric. The techniques also can be
said to control the positioning of the nanotubes within the fabric,
to control the positions of gaps within the nanotube fabric, and to
control the concentration of the nanotubes within the fabric. For
example, these techniques can provide low porosity, high density
fabrics. Further, the techniques can be described as controlling
the gaps of nanotubes within the nanotube fabric. Thus, we have
disclosed techniques to create devices sized to and smaller than
the current lithography limits (for example, less than or equal to
about 20 nm). Low porosity, high density fabrics also can be
created by, for example, filling gaps in the nanotube film with
additional nanotube elements. In other embodiments, a high density
fabric can be created by applying a physical force to the fabric.
Further, the density or porosity of the fabric can be controlled to
create low density and highly porous nanotube fabrics, if so
desired.
Further, the methods of the present disclosure are useful for any
application using nanotube fabrics wherein the concentration of the
individual nanotube elements within the fabric or the dimensions of
gaps within the fabric are required to fit within a preselected
tolerance.
Nanotube Fabrics with Controlled Surface Roughness and Degree of
Rafting
In the previous sections, the use of ionic species within a
nanotube application solution has been described as a means of
controlling the degree of rafting within a nanotube fabric formed
from that nanotube application solution. As discussed above, by
controlling the concentration levels of these ionic species within
a nanotube application solution--as well as controlling the
nanotube density with a nanotube application solution--the degree
of rafting within a nanotube fabric can be selected. In general, as
discussed in detail above, a higher concentration of an ionic
species within a nanotube application solution will tend to
discourage rafting within a nanotube fabric formed from such a
solution, and a lower concentration of ionic species within a
nanotube fabric will tend to promote rafting.
The present disclosure will now go into more detail with respect to
the specific ionic species that can be used to control or select
the degree of rafting within a nanotube fabric, different nanotube
formulations used to form nanotube fabrics, how ionic species
concentration levels are selected for with respect to different
nanotube formulations, and the characterization of specific
nanotube formulations with respect to different ionic species to
select a range of concentration values suited for a particular
application for a given nanotube formulation and selected ionic
species.
The present disclosure will also now describe how fabric
roughness--that is the planarity of the surface of a nanotube
fabric--can be controlled or selected for by using preselected
concentrations of a particular ionic species within a specific
nanotube formulation used to form that nanotube fabric. As will be
discussed in more detail below, highly rafted fabrics, in general,
will tend to be smoother than fabrics with a very low degree or
essentially no rafting. However, in certain applications, a highly
rafted fabric can be undesirable. For example, highly rafted
nanotube fabrics will tend to have higher switching voltages (that
is, the voltage required to adjust the resistivity of a nanotube
fabric from a first state to a second state). Highly rafted fabrics
will also tend to be denser than fabrics with a low degree of
rafting, requiring more individual nanotube elements for a given
volume of fabric. As certain applications--for example, but not
limited to, certain types of two-terminal nanotube switching
elements--require smooth nanotube fabrics with a low degree of
rafting, the present disclosure provides methods for characterizing
a nanotube formulation for a given ionic species. According to the
methods of the present disclosure, this characterization, in
certain applications, provides a nanotube formulation roughness
curve, which plots the expected roughness of a nanotube fabric
formed with a given nanotube formulation against the concentration
level of a given ionic species. As will be discussed in detail
below with respect to FIG. 22 and illustrated within examples
10-23, such a nanotube formulation roughness curve can be used to
select a utilization range of a specific ionic species
concentration for a given nanotube formulation that will provide,
for example, a relatively smooth nanotube fabric with a low degree
of rafting. Methods and parameters for measuring and quantifying
both the degree of rafting within a nanotube fabric and the degree
of surface roughness (or smoothness) within a nanotube fabric will
also be discussed below.
Within certain applications, the surface roughness of a nanotube
fabric and the degree of rafting within a nanotube fabric can have
an effect on the electrical and physical properties of the nanotube
fabric or within a device employing the nanotube fabric. For
example, within two terminal nanotube switching devices (discussed
in detail within the incorporated references), the degree of
rafting within the nanotube fabric used within a device can
influence the switching voltage, resistance, and adjustable
resistance range of that device. Further, the surface roughness of
a nanotube fabric used within two terminal nanotube switching
devices can also impact the uniformity of the distance between the
top and bottom electrodes, which can, in certain embodiments,
affect how the devices function and potentially limit the
scalability of the devices. The surface roughness of a nanotube
fabric can also significantly impact how other material layers
applied over the nanotube fabric form, creating differences in both
electrical and physical characteristics of devices using these
nanotube fabrics. To this end, the methods of the present
disclosure can, in certain aspects, be used to form engineered
nanotube fabrics wherein the surface roughness as well as the
degree of rafting can be reliably controlled by first
characterizing a nanotube formulation and then using that
characterization to adjust the nanotube formulation such that, when
deposited, it forms a nanotube fabric with the a desired surface
roughness and degree of rafting, as required by the needs of a
particular application.
Within the present disclosure, the term "nanotube formulation" is
used to describe nanotube application solutions--that is a
plurality of nanotube elements suspended within a liquid medium
capable of being deposited to form a nanotube fabric--with a
selected set of parameters. Such parameters can include, but are
not limited to, the type of nanotube or nanotubes used within the
application solution, the nanotube wall type (e.g., single walled,
double walled, or multi-walled), the type and degree of
functionalization (or lack thereof) of the nanotube elements, the
lengths and length distribution of the nanotube elements, the
degree to which the nanotube elements are straight or kinked, the
density of the nanotube elements within solution, the purity of the
application solution (e.g., level of metallic impurities), the
chirality of the nanotube elements, and the liquid medium used. As
will be discussed in detail below according to the methods of the
present disclosure, nanotube fabrics formed from two different
nanotube formulations can exhibit different degrees of rafting and
roughness for a given concentration of ionic species. That is to
say, a given concentration of a specific ionic species in a first
exemplary nanotube formulation may produce a smooth fabric with a
significant degree of rafting while the same concentration of that
ionic species in a second exemplary nanotube formulation (with
different parameters than the first) may produce a rough fabric
with a very low degree of rafting. As such, the present disclosure
provides methods for determining a utilizable range for a selected
ionic species within a particular nanotube formulation, with this
utilizable range corresponding to a desired roughness/smoothness
parameter range and degree of rafting range within a nanotube
fabric as fits the needs of a selected application. It should be
noted that such ranges are selected as best fits the needs of a
particular application in which a nanotube fabric is used. For
example, some applications might require a very rough fabric with a
very low degree of rafting, while other application might require a
relatively smooth fabric with a low degree of rafting. The present
disclosure further provides methods for adjusting the concentration
levels of an ionic species within a nanotube formulation into this
utilizable range prior to forming a nanotube fabric such as to
realize the desired properties within the fabric with respect to
smoothness/roughness and the degree of rafting.
It should be noted that while previous discussions of controlling
rafting within nanotube fabrics (in particular, examples 1 through
9), exemplary ionic species concentration thresholds of 10 and 20
ppm as mass of nitrogen atom in the nitrate anion of the ammonium
nitrate were used to select for highly rafted fabrics and fabrics
with a low degree of rafting, respectively, the present disclosure
is not limited in this regard. Indeed, the present disclosure up to
this point (including examples 1 through 9) has been directed at a
range of exemplary nanotube formulations all utilizing the same
type of nanotube (detailed in FIGS. 20A and 20B, and described in
more detail within the discussion of those figures below) and one
particular exemplary ionic species (ammonium nitrate salt). And
while, as described in detail above, within examples 1-9
concentrations of ammonium nitrate salt below 10 ppm as mass of
nitrogen (or .about.0.71 mM ammonium nitrate) provided fabrics with
a relatively high degree of rafting and concentrations of ammonium
nitrate salt above 20 ppm as mass of nitrogen (or .about.1.43 mM
ammonium nitrate) provided fabrics with a relatively low degree of
rafting, these specific concentration levels could be different for
nanotube formulations using different types of nanotubes (such as
those shown in FIGS. 20A-20D, for example) and certainty for
different ionic species within the nanotube formulations. As will
be shown and discussed in more detail below, the utilizable range
for a specific ionic species can vary significantly depending on
the particular nanotube formulation in which it is used. To this
end, the methods of the present disclosure provide methods for both
determining this range for a given ionic species within a given
nanotube formulation and using that range to form nanotube fabrics
with desired smoothness/roughness and degree of rafting
parameters.
FIGS. 17A and 17B each illustrate three steps in an exemplary
nanotube fabric deposition operation (1701-1703 and 1704-1706,
respectively) wherein an exemplary nanotube formulation is being
deposited over a material layer 1750 to form a nanotube fabric.
Within both exemplary operations of FIGS. 17A and 17B, the nanotube
formulation being deposited includes nanotube elements 1710 and
ionic species elements 1730 suspended in liquid medium 1740. It
should be noted that the nanotube formulation used in the exemplary
operation of FIG. 17A is intended to be the same nanotube
formulation used in exemplary operation of FIG. 17B, however the
nanotube formulation within the exemplary operation of FIG. 17A has
been adjusted to have a significantly higher concentration level of
ionic species elements 1730 as compared with the concentration
level of ionic species elements 1730 in the nanotube formulation
within the exemplary operation of FIG. 17B.
It should be noted that exemplary nanotube deposition operations
detailed in FIGS. 17A and 17B are intended as simplified functional
examples used to illustrate the methods of the present disclosure.
For clarity, the relative shapes, sizes, positions, and quantities
of nanotube elements 1710 and ionic species elements 1730 have been
greatly simplified for ease of explanation purposes. That is,
operations detailed in FIGS. 17A and 17B are intended only to be
used to illustrate a relevant mechanism of nanotube fabric
formation with respect to ionic species concentration levels within
a nanotube formulation. As such, no realistic values for nanotube
size or type, actual concentration levels of either nanotube
elements or ionic species, or the type of ionic species is intended
or should be inferred.
Looking now to first process step 1701 of FIG. 17A, a nanotube
formulation has been deposited over material layer 1750. This
deposition process could be a spin coating operation, for example,
as described above with respect to U.S. Pat. No. 7,334,395, but the
methods of the present disclosure are not limited in this regard.
After initial deposition of the nanotube formulation, a significant
volume of liquid medium 1740 remains present such that nanotube
elements 1710 remain suspended in solution with freedom to move
with respect to each other.
Each nanotube element 1710 within process steps 1701-1703 is
surrounded by a dashed line 1720a, which indicates the repulsion
distance of each nanotube element 1710 with respect to other
nanotube elements within the nanotube formulation. According to the
methods of the present disclosure, within certain applications the
concentration level of an ionic species (represented in FIGS. 17A
and 17B as ionic species elements 1730) within a nanotube
formulation directly affects this repulsion distance 1720a in FIG.
17A, as well as repulsion distance 1720b as detailed in FIG. 17B
(discussed further below). Functional groups on the nanotube
elements provide an electrostatic repulsion force, which can, in
certain applications, keep nanotube elements within solution from
coming close together. Without wishing to be bound by theory, the
present disclosure submits that, in certain applications, a
relatively high concentration level of an ionic species within a
nanotube formulation will tend to significantly limit repulsion
distance 1720a around nanotube elements 1710. Within such
applications, ionic species within the solution will screen the
functional groups on the nanotube elements from each other,
significantly limiting the effective repulsion distance
(represented by dashed lines 1720a and 1720b). Similarly, as
detailed in process steps 1704-1706 of FIG. 17B, a relatively low
concentration level of ionic species within a nanotube formulation
will tend to result in a relatively large repulsion distance 1720b
around nanotube elements 1710. As will be described in detail
below, the methods of the present disclosure manage this repulsion
distance (1720a and 1720b, in FIGS. 17A and 17B, respectively) by
adjusting the concentration level of ionic species in a nanotube
formulation into an utilizable range, to realize nanotube fabrics
with a desired surface roughness and a desired degree of rafting.
Further, it should be noted that in certain applications the type
of ionic species used within a nanotube formulation as well as the
way an ionic species crystallizes will affect the roughness of a
nanotube fabric. Ionic species that form larger crystals (1730 in
FIGS. 17A and 17B), for example, will have a greater impact on how
nanotube elements compact on a substrate surface as compared with
ionic species that from smaller crystals.
Looking now to second process step 1702, an intermediate step of
the exemplary nanotube fabric deposition process of FIG. 17A is
shown. Within process step 1702, a significant volume of liquid
medium 1740 has been removed (via, for example, but not limited to,
a spin coating operation). As a result of this decreased volume,
nanotube elements 1710 are forced closer together. However, due to
the significantly limited repulsion distance 1720a present in the
exemplary operation of FIG. 17A, the nanotube elements are able to
move close together and will tend to fit tightly together in a
relatively irregular, haphazard arrangement as their freedom of
movement is reduced due to the decreased volume of the liquid
medium 1740.
It should be noted that within both exemplary processes detailed in
FIGS. 17A and 17B, the concentration level of ionic species within
each nanotube formulation increases between the first and second
process steps (1701 and 1702, respectively, for FIG. 17A, and 1704
and 1705, respectively, for FIG. 17B). While not shown in FIGS. 17A
and 17B for sake of clarity, within certain applications, this
increase in ionic species concentration can significantly reduce
the repulsion distance (1720a and 1720b) of the nanotube elements
within the partially dried nanotube formulation. As such, in these
certain applications, there exists a temporal component to the
fabric deposition process with respect to the degree of rafting
within and the smoothness/roughness of a nanotube fabric formed
from that process. Typically, within such a drying process (as is
shown in FIGS. 17A and 17B), once nanotube elements become
organized (as shown in process steps 1702 and 1705), they will tend
to stay organized as the remaining liquid medium is removed. As
such, according to the methods of the present disclosure, it should
be noted that in certain applications, the method and speed at
which a nanotube formulation is deposited over a material layer and
dried can have an effect on the surface roughness of a nanotube
fabric being formed.
Looking to final process step 1703 of FIG. 17A, substantially all
of liquid medium 1740 has been removed and nanotube elements 1710
have been formed into a nanotube fabric over the surface of
material layer 1750. As described above, due to the low repulsion
distance 1720a caused by the high concentration of ionic species
1730 within the nanotube formulation, nanotube elements 1710 are
able to fit together tightly in an irregular arrangement. This
irregular, haphazard arrangement results in the surface of this
nanotube fabric being significantly rough, as is detailed within
process step 1703.
Looking now to first process step 1704 of FIG. 17B, a nanotube
formulation has again been deposited over material layer 1750. It
should be noted that number, size, and portion of nanotube elements
1710 in first process step 1704 of FIG. 17B are identical to those
shown in first process step 1701 of FIG. 17A. The difference
between the exemplary operations of FIG. 17A (process steps
1701-1703) and 17B (process steps 1704-1706) is that the nanotube
formulation within the exemplary operation of FIG. 17B has a
significantly lower concentration of ionic species elements 1730,
as compared with the nanotube formulation of FIG. 17A. As a result,
the repulsion distance 1720b around nanotube elements 1710 in FIG.
17B is significantly greater than the repulsion distance 1720a
within the exemplary operation of FIG. 17A. As is detailed within
process steps 1705 and 1706 (and described in more detail below),
this increased repulsion distance 1720b results in nanotube
elements 1710 forming into a relatively regular and organized
arrangement, resulting in a smoother nanotube fabric as compared
with the fabric formed by the exemplary operation of FIG. 17A.
Looking now to second process step 1705 of FIG. 17B, a significant
volume of liquid medium 1740 has been removed resulting an
intermediate structure wherein nanotube elements 1710 are forced
closer together due to the reduced volume, similar to process step
1702 of FIG. 17A. Unlike within process step 1702 of FIG. 17A,
however, the increased repulsion distance 1720b limits the movement
of the nanotube elements 1710 and prevents them from forming into a
tight arrangement (as happen in process step 1702), forcing them
into a more organized arrangement.
Looking now to final process step 1706 of FIG. 17B, substantially
all of liquid medium 1740 has been removed and nanotube elements
1710 have been formed into a nanotube fabric over the surface of
material layer 1750 (similar to process step 1703 of FIG. 17A). As
described above, however, due to the significantly large repulsion
distance 1720b caused by the relatively low concentration of ionic
species 1730 within the nanotube formulation, nanotube elements
1710 are kept further apart during the fabric formation process
and, as a result, rendered into a more organized and regular
arrangement. This organized, regular arrangement results in the
surface of the nanotube fabric formed by the exemplary process of
FIG. 17B being significantly smoother that the fabric resulting
from the exemplary process of FIG. 17A, as is detailed within
process step 1703. As is discussed previously within the present
application (notably within examples 1-9, above), within certain
applications, this ordered regular arrangement can result in
nanotube elements 1710 forming into rafts as liquid medium 1740 is
removed.
FIGS. 18A and 18B are a TEM image and a line drawing, respectively,
of a cross-section of a nanotube fabric, formed according to the
methods of the present disclosure, with a relatively high surface
roughness. This relatively rough nanotube fabric (1810a in FIG. 18A
and 1810b in FIG. 18B) is analogous to the nanotube fabric shown in
process step 1703 of FIG. 17A and has been shown here to detail an
example of a nanotube fabric with a relatively rough surface.
Looking to FIG. 18A, nanotube fabric 1810a is formed over a
substrate material layer from a nanotube formulation with a
relatively high concentration level of ionic species (methods used
to determine both high and low concentration levels for a given
ionic species within a particular nanotube formulation will be
discussed in detail below with respect to FIG. 22 and shown within
examples 10-23). A conductive layer 1820a is then formed over
nanotube fabric 1810a. FIG. 18B illustrates both of these material
layers with a line drawing such that the surfaces of both material
layers can be more easily seen. Within FIG. 18B, nanotube fabric
layer 1810b represents nanotube fabric layer 1810a shown in the TEM
image of FIG. 18A, and, similarly, conductive layer 1820b
represents conductive layer 1820a shown in the TEM image of FIG.
18A. Horizontal surface line 1830 is included in the line drawing
of FIG. 18B to provide a reference for the relative surface
roughness of nanotube fabric 1810a/1810b. As can be seen in FIG.
18B, the actual surface of nanotube fabric 1810b varies
significantly above and below horizontal surface line 1830.
Further, the RMS roughness of nanotube fabric 1810a has been
calculated to be 5.54 nm by analyzing an AFM image of the same
fabric using methods that will be described in detail with respect
to examples 10-23 and FIG. 27 below.
FIGS. 19A and 19B are a TEM image and a line drawing, respectively,
of a cross-section of a nanotube fabric, formed according to the
methods of the present disclosure, with a relatively low surface
roughness. This relatively smooth nanotube fabric (1910a in FIG.
19A and 1910b in FIG. 19B) is analogous to the nanotube fabric
shown in process step 1706 of FIG. 17B and has been shown here to
detail an example of a nanotube fabric with a relatively smooth
surface.
Looking to FIG. 19A, nanotube fabric 1910a is formed over a
substrate material layer from a nanotube formulation with a
relatively low concentration level of ionic species (methods used
to determine both high and low concentration levels for a given
ionic species within a particular nanotube formulation will be
discussed in detail below with respect to FIG. 22 and then shown
within examples 10-23). A conductive layer 1920a is then formed
over nanotube fabric 1910a. FIG. 19B illustrates both of these
material layers with a line drawing such that the surfaces of both
material layers can be more easily seen. Within FIG. 19B, nanotube
fabric layer 1910b represents nanotube fabric layer 1910a shown in
the TEM image of FIG. 19A, and, similarly, conductive layer 1920b
represents conductive layer 1920a shown in the TEM image of FIG.
19A. Horizontal surface line 1930 is included in the line drawing
of FIG. 19B to provide a reference for the relative surface
roughness of nanotube fabric 1910a/1910b. As can be seen in FIG.
19B, the actual surface of nanotube fabric 1910b does not vary
significantly above or below horizontal surface line 1930,
especially as compared to FIG. 18B. Further, the RMS roughness of
nanotube fabric 1910a has been calculated to be 0.74 nm by
analyzing an AFM image of the same fabric using methods that will
be described in detail with respect to examples 10-23 and FIG. 27
below and is significantly less than the roughness calculated for
the nanotube fabric 1810a of FIG. 18A.
As described above, the parameters of a particular nanotube
formulation can greatly affect the concentration levels of a given
ionic species required to promote or discourage rafting within a
nanotube fabric formed from that formulation and also the surface
roughness of that fabric. That is to say, as will be shown in
detail below, a particular nanotube formulation, as defined by the
present disclosure, and a given ionic species will be associated
with a specific nanotube formulation roughness curve, that curve
defined by the different parameters of the nanotube formulation
itself. One of the significant parameters of a nanotube formulation
that can significantly affect the shape of a nanotube formulation
roughness curve is the type of nanotube used in the formulation. To
this end, FIGS. 20A-20F are TEM images providing examples of the
different types of nanotubes used within the examples of the
present disclosure.
Looking to FIGS. 20A and 20B, a first exemplary type of nanotube is
shown in SEM images 2001 and 2002, respectively. This first
exemplary type of nanotube is used in examples 1-9 above. The
nanotubes shown in FIGS. 20A and 20B are predominately
double-walled carbon nanotubes, that are relatively long and
straight (that is, have few bends, kinks or curves). This first
exemplary type of nanotube had a median length of 290 nm and a 95th
percentile length of 810 nm. As described above with respect to
examples 1-9, nanotubes of this type were functionalized and
purified, then formed into nanotube formulations as described
above. As detailed above with respect to examples 1-9, the nanotube
formulations using this nanotube type and ammonium nitrate salt as
an ionic species, generally, tended to raft below ionic species
concentration levels of 10 ppm and had lower incidences of rafting
with ionic species concentration levels above 20 ppm. Although, it
can also be seen from the data with examples 1-9 that the density
of nanotube within each nanotube formulation, also had an effect on
the degree of rafting. It should be noted that examples 1-9 do not
characterize or quantify the surface roughness of any of the
fabrics generated. Examples 10-23 have been included in the present
disclosure to provide examples and data for different formulations
in terms of surface roughness.
Looking now to FIGS. 20C and 20D, a second exemplary type of
nanotube is shown in SEM images 2003 and 2004, respectively. This
second exemplary type of nanotube is used within nanotube
formulation "B" as described within examples 10-16, discussed in
detail below. The nanotubes shown in FIGS. 20C and 20D are
predominately singled-walled carbon nanotubes that are
significantly shorter that the first exemplary nanotube type (FIGS.
20A and 20B) but longer than the third exemplary nanotube type
(FIGS. 20E and 20F, discussed below) and straight (that is, have
few bends, kinks or curves). This second exemplary type of nanotube
had a median length of 187 nm and a 95th percentile length of 494
nm. As described within the discussion of examples 10-16, nanotubes
of this type were functionalized and purified (via methods
described within the discussion of FIG. 23A below) and formed into
nanotube formulations. Formulations using this type of nanotube
were then tested with ammonium nitrate salt (NH.sub.4NO.sub.3) in
examples 11-13 to realize nanotube formulation roughness curve 2610
in FIG. 26A and tetramethyl ammonium formate (TMA Fm) in examples
14-16 to realize nanotube formulation roughness curve 2620 in FIG.
26B. The results of these curves (2610 and 2620) will be described
in detail within the discussion of FIGS. 26A and 26B below.
Looking now to FIGS. 20E and 20F, a third exemplary type of
nanotube is shown in SEM images 2005 and 2006, respectively. This
third exemplary type of nanotube is used within nanotube
formulation "C" as described within examples 17-23, discussed in
detail below. The nanotubes shown in FIGS. 20E and 20F are
predominately multi-walled carbon nanotubes, each of which has a
plurality of kinks and bends, and are significantly short as
compared to the first and second exemplary type of nanotubes shown
in FIGS. 20A and 20B and used within examples 1-9 and FIGS. 20C and
20D and used within examples 10-16. This second exemplary type of
nanotube had a median length of 132 nm and a 95th percentile length
of 260 nm. As described within the discussion of examples 17-23,
nanotubes of this type were functionalized and purified (via
methods described within the discussion of FIG. 23A below) and
formed into nanotube formulations. Formulations using this type of
nanotube were then tested with ammonium nitrate salt
(NH.sub.4NO.sub.3) in examples 18-20 to realize nanotube
formulation roughness curve 2630 in FIG. 26C and tetramethyl
ammonium formate (TMA Fm) in examples 21-23 to realize nanotube
formulation roughness curve 2640 in FIG. 26D. The results of these
curves (2630 and 2640) will be described in detail within the
discussion of FIGS. 26C and 26D below.
As described in above, while examples 1-9 described above use
ammonium nitrate salt as an ionic species to adjust and control
rafting in nanotube formulations, the methods of the present
disclosure are not limited in this regard. Indeed, as discussed
above, ionic species, as defined by the present disclosure, can
include, but are not limited to, ammonium salts, nitrate salts,
ammonium nitrate salts, ammonium formate, ammonium acetate,
ammonium carbonate, ammonium bicarbonate, ionic organic species,
ionic polymers, and inorganic salts. Further, cations well suited
for use with the methods of the present disclosure include, but are
not limited to: ammonium; all quaternary ammonium functionalities
(e.g., tetraalkylammoniums such as, but not limited to,
tetramethylammonium, tetraethylammonium, tetrapropylammonium, and
dimethyldiethylammonium); acids of all primary, secondary, and
tertiary aliphatic amines; acids of cylic amines (such as, but not
limited to, piperidinium and pyrrolidinium); Cylic, aromatic
quartenary amines (such as, but not limited to, imidazolium and
pyridinium); and short chain alkyl phosphonium ions. Further,
anions well suited for use with the methods of the present
disclosure include, but are not limited to: bases of all soluble
organic acids containing only nitrogen (N), oxygen, carbon (C), and
hydrogen (H); simple soluble aliphatic carboxylic acids (such as,
but not limited to, carbonate, formate, acetate, and proprionate);
non-zwitterionic complex organic acids (such as, but not limited
to, aromatic acids such as benzoate); nitrate; and phosphate. For
certain applications wherein electronic fabrication cleanroom
standards are not required (for example, but not limited to,
nanotube fabrics used for material coatings), inorganic ionic
species can be used with the methods of the present disclosures.
Such nonvalent inorganic ionic species include, but are not limited
to, cations of sodium, calcium, potassium, and magnesium and anions
of chloride, bromide, sulfate, nitrate, and carbonate.
To this end, FIG. 21 provides a table 2100 of cations and anions
which can be used to form a plurality of ionic species well-suited
for use with the methods of the present disclosure. It should be
noted that this table is intended to provide a list of exemplary
ionic species and the methods of the present disclosure should not
be limited to this list. As described by the present disclosure,
each of these ionic species can result in a different nanotube
formulation roughness curve for a given nanotube formulation. As
such, the present disclosure provides methods for characterizing
nanotube formulations to generate nanotube formulation roughness
curves (as described within the discussion of FIG. 24 below) for a
specific ionic species used within a specific nanotube
formulation.
As previously discussed, the earlier sections of the present
disclosure as well as examples 1-9 describe methods for controlling
the degree of rafting within a nanotube fabric. The present
disclosure now describes methods for not only controlling the
degree of rafting within a nanotube fabric but also for selecting
the surface roughness of the nanotube fabric at the same time. As
has been described above and will be shown within examples 10-23,
the generation of a nanotube formulation roughness curve for a
given nanotube formulation and ionic species allows for control
(via adjustment of the ionic species concentration level) of the
surface roughness of a nanotube fabric and the degree of rafting
within a nanotube fabric.
FIG. 22 is a labeled example of a nanotube formulation roughness
curve 2200 intended to illustrate how such a curve can be used to
adjust the ionic species concentration of a nanotube formulation to
produce a nanotube fabric with a desired surface roughness and
degree of rafting. It should be noted that the exemplary nanotube
formulation roughness curve 2200 of FIG. 22 as well as nanotube
formulation roughness curves detailed in the discussions of
examples 10-23 (FIGS. 26A-26D) are targeted at providing relatively
smooth nanotube fabrics with a low degree of rafting. However, the
methods of the present disclosure are not limited in this regard.
As will be described below, the selection of utilizable range
within a nanotube formulation roughness curve will be dependent on
the needs and requirements of a specific application. For example,
certain applications might require a highly rafted fabric. Other
applications might require a very rough fabric. As will be shown
below, the requirements of a specific application are used to set
threshold values, which are then used to define a utilizable range
2240 within a nanotube formulation roughness curve. This utilizable
range 2240 then provides a target ionic species concentration level
zone on the curve indicative of concentration values that will
provide a nanotube fabric that meets the given requirements.
Looking now to FIG. 22, curve 2200 plots the concentration of the
selected ionic species in millimoles (mM) on the x-axis and the RMS
roughness value in nanometers (nm) of a nanotube fabric formed with
a nanotube formulation at a given concentration on the y-axis. In
practice, such a nanotube formulation roughness curve is generated
experimentally by forming a plurality of identical nanotube
formulations, adjusting the ionic species concentration level in
each of these nanotube formulations to a different value, forming a
nanotube fabric with each of the differently adjusted nanotube
formulations, and then measuring the RMS roughness of and degree of
rafting within each of the resulting nanotube fabrics. This method
of generating a nanotube formulation roughness curve for a given
nanotube formulation and ionic species is detailed in FIG. 24 and
described in more detail in the discussion of that figure below.
The nanotube formulation roughness curves of FIGS. 26A-26D (2610,
2620, 2630, and 2640), which plot the results of examples 10-23 to
realize four different nanotube formulation roughness curves, were
each created using four data points realized experimentally in this
manner. However, the methods of the present disclosure are not
limited in this regard. Indeed, any number of data points can be
used to produce a nanotube formulation roughness curve, including,
but not limited to, 2, 3, 4, 5, 10, 15, 20, 50, or 100. This is to
say, the number of data points generated and used to create a
nanotube formulation roughness curve is only limited by the
specific needs of an application.
Looking back now to FIG. 22, curve 2210 is imagined to be plotted
through a number of experimentally obtained data points. As curve
2210 is intended as an illustrative example, no actual data was
used to generate this curve. However, the nanotube formulation
roughness curves of FIGS. 26A-26D provide curves generated through
real experimentally obtained data. A horizontal line 2220 is drawn
through curve 2210 and is indicative of the acceptable roughness
threshold for a selected application. As indicated by the arrows on
the plot, any points on the curve above this line 2220 will have a
surface roughness greater than this selected threshold, and any
point on the curve below this line with have a roughness lower than
this threshold. Similarly, a vertical line 2230 is drawn through
curve 2210 and is indicative of the acceptable degree of rafting
threshold for a selected application. As indicated by the arrows on
the plot, any points to the left of this line 2230 will have a
degree of rafting higher than this threshold, and any points to the
right of this line 2230 will have a degree of rafting lower than
this threshold. The points on the curve 2210 that cross these two
threshold lines (2220 and 2230) define a utilizable range 2240
within the nanotube formulation roughness curve 2200. By adjusting
an ionic species concentration level within a nanotube formulation
to within this utilizable range 2240, nanotube fabrics can be
formed with the surface roughness and degree of rafted required for
a selected application.
As is detailed within exemplary nanotube formulation curve 2200,
lower concentrations of ionic species within a nanotube formulation
generally tend to result in nanotube fabrics with smoother surfaces
and a higher degree of rafting, while higher concentrations of
ionic species within a nanotube formulation generally tend to
result in nanotube fabrics with rougher surfaces and a low degree
of rafting. Within certain applications (for example, but not
limited to, two-terminal nanotube switching devices, as described
in U.S. Pat. No. 7,781,862 described above), it can be advantageous
to use nanotube fabrics that are both relatively smooth and exhibit
a low degree of rafting. The exemplary utilizable range 2240 of
nanotube formulation roughness curve 2200 is selected to meet such
a design requirement. However, as described above, the methods of
the present disclosure are not limited in this regard. Indeed, in
certain applications, wherein, for example, a very rough fabric is
required, utilization zone 2240 could be drawn to define points on
curve 2210 which fell above horizontal line 2220.
It should also be noted, that in certain applications a nanotube
formulation roughness curve can be calculated once for a given
nanotube formulation and ionic species combination, and then reused
for operations using nanotube formulations with the same
parameters. For example, within a large scale manufacturing
operation wherein the parameters of a nanotube formulation could be
reliably controlled and the methods for depositing that nanotube
formulation also well-known and controlled, a nanotube formulation
roughness curve could be produced experimentally a single time on
an initial nanotube formulation, and then the resulting utilization
range used on all subsequent builds of nanotube formulations with
matching parameters used within the process. In this way, the
methods of the present disclosure can be used to provide design
parameters for a large scale manufacturing process that includes
the large scale production of nanotube fabrics with a controlled
and repeatable surface roughness and degree of rafting
characteristics.
FIG. 23A is a flow chart detailing a method 2301 for producing a
carbon nanotube (CNT) fabric with a preselected surface roughness
and degree of rafting according to the methods of the present
disclosure. The method begins with process step 2310 wherein Raw
CNT Material is selected. As described above with respect to FIGS.
20A-20F, different types of nanotubes (for example, but not limited
to, single walled, double walled, multiwalled, long, short,
straight, kinked, metallic, semiconducting, and mixtures thereof)
are selected as best befits the needs of a particular application.
Within first process step 2310, the type or types of nanotube
required is selected and produced in the required quantity.
In next process step 2315, the selected Raw CNT Material 2310 is
processed and suspended in a liquid medium to form an initial
nanotube application solution. Carbon nanotube (CNT) raw materials
normally come in come in a solid non-solubilized form. They do not
readily form stable, non-precipitating suspensions in typical
solvating media, such as water, alcohols, esters, and ethers. In
order to integrate the manufacturing of nanotube devices with
existing semiconductor facilities, it is often necessary to prepare
a spin- or spray-coatable nanotube solution or dispersion before
use. For example, a nanotube powder has to be suspended, dispersed,
solvated, or mixed in a liquid medium or solvent, so as to form a
nanotube solution or dispersion. In some cases, this liquid medium
could be water (including, but not limited to, distilled water or
deionized water). In other cases, this liquid medium could be a
non-aqueous solvent, such as, but not limited to, ethyl lactate,
dimethyl sulfoxide (DMSO), monomethyl ether, 4-methyl-2 pentanone,
N-methylpyrrolidone (NMP), t-butyl alcohol, methoxy propanol,
propylene glycol, ethylene glycol, gamma-butyrolactone, benzyl
benzoate, salicylaldehyde, tetramethyl ammonium hydroxide, and
esters of alpha-hydroxy carboxylic acids. In other embodiments, the
liquid medium may contain or be predominantly a non-halogenated
solvent. To this end, CNT Processing step 2315 can include, but is
not limited to, functionalizing of the nanotube elements, selecting
the nanotube density of the application solution (via, for example,
cutting of the nanotube elements and/or filtering operations),
selecting the length distribution of the nanotube elements, and
adjusting the pH level within the solution. Examples of such
nanotube processing operations can be found in U.S. Pat. No.
9,634,251 and U.S. patent application Ser. No. 14/033,158 (now
published as US2015/0086771), both of which are hereby included by
reference in their entirety.
In a next processing step 2317, the initial nanotube application
solution is purified using one or more purification steps to
realize Carbon Nanotube (CNT) Formulation 2320. Purification
process step 2317 can include one or more purification operation
such as, but not limited to, a cross-flow filtration (CFF) process,
a vacuum filtration process, sonication, a depth filter process,
centrifugation, treatments of certain chemicals, and/or any
combinations thereof. Dependent on the needs of a particular
application, such purification processes can be effective in
producing highly pure nanotube formulations--that is, formulations
substantially free of surfactants, metallic impurities, other
additives etc. Methods for purifying nanotube application solutions
are described in U.S. Pat. Nos. 9,650,732 and 10,069,072, both of
which are hereby included by reference in their entirety.
It should be noted that CNT Processing step 2315 and Purification
step 2317 can be, in certain applications, be performed together,
simultaneously, or have steps interspersed. That is, within such
applications raw CNT materials 2310 may first go through a
processing step (a functionalization step, for example), then go
through a purification step (acid treatment, for example), then go
through a second process step (length adjustment, for example),
followed by a second purification step (a cross-flow filtration
process, for example). Additionally, some treatments to an initial
CNT application solution can serve as both a CNT Processing step
2315 and a Purification step 2317 (acid treatment or filtering, for
example). As such, while FIG. 23A depicts these two process steps
(2315 and 2317) as being performed separately and in a sequence,
this is done solely for ease of explanation and the methods of the
present disclosure should not be limited in this regard. Indeed, as
discussed above, the processing of raw CNT materials and the
purification of those materials can be performed within a plurality
of individual process steps performed in any order or even
simultaneously.
Further, in certain applications, volumes of ionic species material
can be introduced to the initial application solution during CNT
Processing process step 2315 and Purification process step 2317.
Within such applications, CNT Formulation 2320 includes non-zero
concentration levels of one or more ionic species immediately
subsequent to process steps 2315 and 2317. In some applications,
this "preloaded" ionic species material is introduced into the
initial application solution as part of the ionic species
concentration level adjustment process (introducing a desired ionic
species at an initial concentration level, for example). In other
applications, the introduction of ionic species material at this
point in the process (process steps 2315 and 2317) will simply be
an effect of the processing or purification processes used. In
either case, as described below, the methods of the present
disclosure are well suited to either adjust the concentration level
of the preloaded ionic species to a desired target level (in the
case wherein the preloaded ionic species is of a desired type for a
given application) or remove the preloaded ionic species and
replace it with a different ionic species type (in the case wherein
the preloaded ionic species is of an undesired type for a given
application).
Within the next several process steps the ionic species
concentration level of CNT Formulation 2320 is adjusted according
to the methods of the present disclosure such that the ionic
species concentration level falls within the utilization range as
required by the specific needs of the application in which the
nanotube fabric being formed will be used. The adjustment process
first starts by either generating Nanotube Formulation Roughness
curve 2330 for CNT Formulation 2320 or by using such a curve that
has been previously generated for CNT Formulation 2320 (as
described above). Within process step 2335, the utilization range
obtained from Nanotube Formulation Roughness Curve 2330 is used to
select a target ionic species concentration level. Within
sub-method 2340, the ionic species concentration level of CNT
Formulation 2320 is adjusted (using one or more cycles) to this
target value to realize Adjusted CNT Formulation 2350.
Sub-method 2340 includes a plurality of process steps,
which--dependent on the needs of a particular application--can be
repeated multiple times. In some applications, a first ionic
species type is removed (all or in part) from CNT Formulation 2320
in a first operation, then a second ionic species type is added in
a second operation such that the second ionic species type is
present in Adjusted CNT Formulation 2350 at the target
concentration. In other applications, CNT Formulation 2320 is
substantially devoid of ionic species (having an ionic species
concentration of essentially zero) immediately subsequent to CNT
Processing step 2315 and Purification steps 2317, and sub-method
2340 used (in a single iteration or within multiple iterations) to
add in a selected ionic species to the target concentration level.
In still other applications, CNT Formulation 2320 will have the
desired ionic species present at some initial concentration level
immediately subsequent to CNT Processing step 2315 and Purification
steps 2317, and sub-method 2340 used (within a single iteration or
within multiple iterations) to either raise or lower this initial
concentration level to the target concentration level.
Sub-method 2340 first includes process step 2342 wherein the
concentration level of ionic species within the CNT Formulation
2320 is adjusted. Process step 2346 then determines the new
concentration level of ionic species present in the nanotube
formulation subsequent to this adjustment process. Finally, process
step 2348 determines if further adjustment of the ionic species
concentration level is required. If more adjustment is needed,
sub-method 2340 begins again with process step 2342. This loop
continues until the selected ionic species with CNT Formulation
2320 has a concentration level within an acceptable range of the
target concentration level, at which point CNT formulation 2320 has
been sufficiently adjusted to realize Adjusted CNT Formulation
2350. Methods for adjusting the ionic species concentration level
(that is, process step 2342) are described within the discussions
of FIGS. 23B-23D below and include, but are not limited to,
cross-flow filtration processes, ion exchange processes, dialysis,
and chemical treatment.
In a next process step 2355, adjusted CNT formulation 2355 is
processed through one or more final formulation adjustment steps
(such as, but not limited to, the addition of surfactants or
molecular additives as described in U.S. Pat. No. 9,634,251) and
final purification steps to realize Purified Adjusted CNT Solution
2360. In next process step 2365, Purified Adjusted CNT Solution
2360 is deposited (via, for example, but not limited to, a spin
coating operation) to form CNT Fabric 2370. As Purified Adjusted
CNT Solution 2360 has an ionic species concentration level
corresponding to a selected surface roughness parameter and/or a
selected degree of rafting, CNT Fabric 2370 will exhibit these
properties. In this way, the present disclosure provides a method
for forming a nanotube fabric with a selected surface roughness and
degree of rafting.
FIG. 23B is a flow chart 2302 depicting a first exemplary Ionic
Species Adjustment Process 2342b according to the methods of the
present disclosure, which is imagined to be designed to reduce the
ionic species concentration level of CNT Formulation 2320 to a very
low or substantially zero value. First exemplary Ionic Species
Adjustment Process 2342b is intended to be an expanded and more
detailed version of process step 2342 in FIG. 23A (as are second
and third exemplary Ionic Species Adjustment Processes 2342c within
FIG. 23C and 2342d within FIG. 23D, respectively, discussed further
below), which takes CNT Formulation 2320 and adjusts the ionic
species concentration level within that formulation to realize
Adjusted CNT Formulation 2350, as described above with respect to
FIG. 23A.
First exemplary Ionic Species Adjustment Process 2342b is comprised
of two sub-processes: a Crossflow Filtration sub-process 2380b and
an Ion Exchange sub-process 2390b. Crossflow Filtration process
2380b is first used to remove a significant volume of ionic species
from CNT Formulation 2320. Then, Ion Exchange sub-process 2390b is
used to further reduce the concentration level of the remaining
ionic species within the nanotube formulation (as described within
the discussion of FIG. 23A above). In this way, the concentration
of ionic species present within CNT Formulation 2320 is adjusted to
a very low or substantially zero level.
It should be noted that within FIG. 23B, Crossflow Filtration
sub-process 2380b and Ion Exchange sub-process 2390b are depicted,
for ease of explanation, as each being performed only a single
time. However, as described above within the discussion of FIG.
23A, the methods of the present disclosure are not limited in this
regard. Indeed, in some applications Crossflow Filtration
sub-process 2380b could be performed multiple times prior to the
start of Ion Exchange sub-process 2390b. Similarly, Ion Exchange
sub-process 2390b could also be, within certain applications,
performed multiple times subsequent to the conclusion of one or
more Crossflow Filtration sub-process 2380b iterations. Further,
the entire Ionic Species Adjustment process 2342b could be, within
certain applications, looped and performed multiple times (as is
depicted in FIG. 23A) to achieve a desired ionic species
concentration level.
As depicted in FIG. 23B, Crossflow Filtration sub-process 2380b is
comprised of a plurality of sub-process steps. CNT Formulation 2320
is first dewatered in sub-process step 2382b such that the CNT
material within the formulation is compacted onto a filtration
membrane in process step 2384b. In this way, a significant
volume--or in some cases, substantially all--of any ionic species
material present within CNT Formulation 2320 is separated from the
CNT material, as the ionic species material passes through the
filter membrane while the CNT material is compacted onto the filter
membrane. In a next sub-process step 2386b, the filtration membrane
is purged with Recovery Solution 2387b. As Crossflow Filtration
sub-process 2380b is intended to reduce the concentration level of
ionic species within CNT Formulation 2320, Recovery Solution 2387b
is selected to be a low-salt containing material, such as, but not
limited to, deionized water. In this way, the compacted CNT
material is recovered back into a formulation with a significantly
lower ionic species concentration as compared to CNT formulation
2320. As described above, Crossflow Filtration sub-process 2380b
can be performed a single time, as is depicted in FIG. 23B, or
repeated once or more to further reduce the ionic species
concentration level present in CNT Formulation 2320.
Looking now to Ion Exchange sub-process 2390b, the ionic species
concentration level of CNT Formulation 2320 is further reduced
subsequent to the concentration reduction performed by Crossflow
Filtration sub-process 2380b. Within certain applications, Ion
Exchange sub-process 2390b comprises a series of individual ion
exchange steps, each of which flow CNT Formulation 2320 through a
resin column containing a specific type of ion exchange resin.
These ion exchange steps can target the removal of a specific ion
(for example, but not limited to, FE.sup.2+ or CA.sup.2+) or a
broad category of ions (for example, but not limited to, all anions
or all cations). In certain applications, a mixed bed ion exchange
can also be used to remove both anions and cations within a single
process step.
As first exemplary Ionic Species Adjustment process 2342b is
imagined to be focused on reducing ionic species concentration
levels, it is imagined that Anion Exchange sub-process step 2392b
first removes substantially all anions present within the
formulation using, for example, an OH.sup.- charged column.
Subsequently, Cation Exchange sub-process step 2394b then removes
substantially all cations present within the formulation using, for
example, a H.sup.+ charged column. As described above, Ion Exchange
sub-process 2390b can be performed a single time, as is depicted in
FIG. 23B, or repeated once or more to further reduce the ionic
species concentration level present in CNT Formulation 2320.
Further, while FIG. 23B depicts Anion Exchange sub-process step
2392b being performed prior to Cation Exchange sub-process step
2394b, the methods of the present disclosure are not limited in
this regard. Indeed, as described above, in certain applications
Cation Exchange sub-process step 2394b could be performed prior to
Anion Exchange sub-process step 2392b. Further, in certain
applications both the cation exchange and anion exchange
sub-process steps could be performed together using a mixed bed ion
exchange process.
In this way, a significant volume (or in, some cases, substantially
all) of ionic species present in CNT Formulation 2320 can be
removed using a combination of Crossflow Filtration sub-process
2380b and Ion Exchange sub-process 2390b, resulting in Adjusted CNT
Formulation 2350, which, within this particular ionic species
adjustment process example 2302, has a very low (or substantially
zero) concentration level of ionic species.
It should be noted that while first exemplary Ionic Species
Adjustment Process 2342b is depicted as first using a Crossflow
Filtration sub-process 2380b followed by a subsequent Ion Exchange
sub-process 2390b, the methods of the present disclosure are not
limited in this regard. Indeed, in certain applications an ionic
species adjustment process targeted at reducing ionic species
concentration within a CNT formulation could include only Crossflow
Filtration sub-process step 2380b (performed once or multiple
times) or only Ion Exchange sub-process step 2390b (performed once
or multiple times). Further, within certain applications such an
ionic species adjustment process could perform Ion Exchange
sub-process 2390b (performed once or multiple times) prior to
Crossflow Filtration sub-process step 2380b (performed once or
multiple times).
FIG. 23C is a flow chart 2303 depicting a second exemplary Ionic
Species Adjustment Process 2342c according to the methods of the
present disclosure, which is imagined to be designed to
substantially remove a first type of ionic species from CNT
Formulation 2320 and replace it with a second type of ionic species
at a selected concentration level. Second exemplary Ionic Species
Adjustment Process 2342c is intended to be an expanded and more
detailed version of process step 2342 in FIG. 23A (as are first and
third exemplary Ionic Species Adjustment Processes 2342b within
FIG. 23B and 2342d within FIG. 23D, respectively), which takes CNT
Formulation 2320 and adjusts the ionic species concentration level
within that formulation to realize Adjusted CNT Formulation 2350,
as described above with respect to FIG. 23A.
Second exemplary Ionic Species Adjustment Process 2342c is
comprised of two sub-processes: a first Crossflow Filtration
sub-process 2380c ("Crossflow Filtration I") and a second Crossflow
Filtration sub-process 2390c ("Crossflow Filtration II"). First
Crossflow Filtration sub-process 2380c is first used to remove a
significant volume of a first ionic species from CNT Formulation
2320. This first ionic species is imagined to be present with CNT
Formulation 2320 subsequent to CNT Processing 2315 and Purification
2317 steps of FIG. 23A and to be undesired within Adjusted CNT
Formulation 2350. Then, second Crossflow Filtration sub-process
2390b is used to introduce a second ionic species type into CNT
Formulation 2320 at the target concentration level (as determined
in process step 2335 in FIG. 23A). In this way, the concentration
level of an undesired ionic species is significantly lowered (or,
in certain applications, made essentially zero) within CNT
Formulation 2320 and a desired ionic species is introduced into CNT
Formulation 2320 and adjusted to the preselected target level (as
determined in process step 2335 in FIG. 23A).
It should be noted that within FIG. 23C, both first Crossflow
Filtration sub-process 2380c and second Crossflow Filtration
sub-process 2390c are depicted, for ease of explanation, as each
being performed only a single time. However, as described above
within the discussion of FIG. 23A, the methods of the present
disclosure are not limited in this regard. Indeed, in some
applications first Crossflow Filtration sub-process 2380c could be
performed multiple times prior to the start of second Crossflow
Filtration sub-process 2390c. Similarly, second Crossflow
Filtration sub-process 2390c could also be, within certain
applications, performed multiple times subsequent to the conclusion
of one or more first Crossflow Filtration sub-process 2380c
iterations.
As depicted in FIG. 23C, first Crossflow Filtration sub-process
2380c is comprised of a plurality of sub-process steps. CNT
Formulation 2320 is first dewatered in sub-process step 2382c such
that the CNT material within the formulation is compacted onto a
filtration membrane in process step 2384c. In this way, a
significant volume--or in some cases, substantially all--of any
ionic species material present within CNT Formulation 2320 is
separated from the CNT material, as the ionic species material
passes through the filter membrane while the CNT material is
compacted onto the filter membrane. In a next sub-process step
2386c, the filtration membrane is purged with Recovery Solution
2387c. As first Crossflow Filtration sub-process 2380c is intended
to reduce the concentration level of ionic species within CNT
Formulation 2320, Recovery Solution 2387c is selected to be a
low-salt containing material, such as, but not limited to,
deionized water. In this way, the compacted CNT material is
recovered back into a formulation with a significantly lower ionic
species concentration as compared to CNT formulation 2320. As
described above, first Crossflow Filtration sub-process 2380c can
be performed a single time, as is depicted in FIG. 23C, or repeated
once or more to further reduce the ionic species concentration
level present in CNT Formulation 2320.
Second Crossflow Filtration sub-process 2390c is comprised of a
plurality of sub-process steps, similar to those discussed above
with respect to first Crossflow Filtration sub-process 2380c.
Subsequent to processing through first Crossflow Filtration
sub-process 2380c, CNT Formulation 2320 (at list point exhibiting a
very low or zero ionic species concentration level) is again
dewatered in sub-process step 2392c such that the CNT material
within the formulation is compacted onto a filtration membrane in
process step 2394c. In a next sub-process step 2396c, the
filtration membrane is purged with Recovery Solution 2397c. As
second Crossflow Filtration sub-process 2390c is intended to
introduce a desired ionic species at the target ionic species
concentration level (as determined within process step 2335 of FIG.
23A) into CNT Formulation 2320, Recovery Solution 2397c is
preloaded with a selected volume of the Selected Ionic Species
2395c prior to process step 2396c. In this way, the compacted CNT
material is recovered back into a formulation with along with a
volume of ionic species selected to provide the target
concentration level within the formulation. As described above,
second Crossflow Filtration sub-process 2390c can be performed a
single time, as is depicted in FIG. 23C, or repeated once or more
to further reduce the ionic species concentration level present in
CNT Formulation 2320.
In this way, a significant volume (or in, some cases, substantially
all) of an undesired ionic species present in CNT Formulation 2320
can be removed and a desired ionic species added at a selected
concentration level using a combination of Crossflow Filtration
sub-processes (2380c and 2390c), resulting in Adjusted CNT
Formulation 2350, which, within this particular ionic species
adjustment process example 2303, has a concentration level of
desired ionic species set at a desired target level (as determined
by process step 2335 in FIG. 23A).
It should be noted that while second exemplary Ionic Species
Adjustment Process 2342c is depicted as using two separate
Crossflow Filtration sub-processes (first Crossflow Filtration
sub-process 2380c followed by a second Crossflow Filtration
sub-process 2390c), the methods of the present disclosure are not
limited in this regard. Indeed, in certain applications the removal
of a first undesired ionic species and the introduction of a second
desired ionic species into a CNT formulation could be performed
within a single crossflow filtration process. In such an operation,
sub-process steps analogous to process step 2382c and 2384c
(dewatering of the CNT formulation and compacting of the CNT
material onto a filter membrane) could be used to first remove an
undesired ionic species from the system, and then sub-process steps
analogous to 2395c, 2397c, and 2396c (purging the filter membrane
with a recovery solution preloaded with a selected volume of a
second desired ionic species) could be used to introduce a desired
ionic species into the system immediately subsequent to removing
the first undesired ionic species. The depiction of these two
sub-process steps as separate Crossflow Filtration sub-processes
(2380c and 2390c) in FIG. 23C is done purely for ease of
explanation, and the present disclosure should not be limited in
this regard.
FIG. 23D is a flow chart 2304 depicting a third exemplary Ionic
Species Adjustment Process 2342d according to the methods of the
present disclosure, which is imagined to be designed to first
exchange an undesired first type of ionic species within CNT
Formulation 2320 with a desired second type of ionic species (using
Ion Exchange sub-process 2380d), and then lower the concentration
level of that second type of ionic species within the formulation
to a desired target level (using Crossflow Filtration sub-process
2390d). Third exemplary Ionic Species Adjustment Process 2342d is
intended to be an expanded and more detailed version of process
step 2342 in FIG. 23A (as are first and second exemplary Ionic
Species Adjustment Processes 2342b within FIG. 23B and 2342c within
FIG. 23C, respectively), which takes CNT Formulation 2320 and
adjusts the ionic species concentration level within that
formulation to realize Adjusted CNT Formulation 2350, as described
above with respect to FIG. 23A.
Third exemplary Ionic Species Adjustment Process 2342d is comprised
of two sub-processes: an Ion Exchange sub-process 2380d and a
Crossflow Filtration sub-process 2390d. Ion Exchange sub-process
2380d is first used to replace a first ionic species present within
CNT Formulation 2320 with a second ionic species. Crossflow
Filtration sub-process 2390d is then used, in a subsequent
sub-process step to reduce the concentration level of the second
ionic species within the CNT formulation. Within the present
example, this first ionic species is imagined to be present with
CNT Formulation 2320 subsequent to CNT Processing 2315 and
Purification 2317 steps of FIG. 23A and to be undesired within
Adjusted CNT Formulation 2350, while the second ionic species is
imagine to be the desired ionic species, with a target
concentration value determined in process step 2335 of FIG. 23A. In
this way, the concentration level of an undesired ionic species is
significantly lowered (or, in certain applications, made
essentially zero) within CNT Formulation 2320 and a desired ionic
species is introduced into CNT Formulation 2320 and adjusted to the
preselected target level (as determined in process step 2335 in
FIG. 23A).
It should be noted that within FIG. 23D, Ion Exchange sub-process
2380d and Crossflow Filtration sub-process 2390d are depicted, for
ease of explanation, as each being performed only a single time.
However, as described above within the discussion of FIG. 23A, the
methods of the present disclosure are not limited in this regard.
Indeed, in some applications Ion Exchange sub-process 2380d could
be performed multiple times prior to the start of Crossflow
Filtration sub-process 2390d. Similarly, Crossflow Filtration
sub-process 2390d could also be, within certain applications,
performed multiple times subsequent to the conclusion of one or
more Ion Exchange sub-process 2380d iterations.
As depicted in FIG. 23D, Ion Exchange sub-process 2380d is
comprised of a plurality of sub-process steps. Within certain
applications, Ion Exchange sub-process 2380b comprises a series of
individual ion exchange steps, each of which flow CNT Formulation
2320 through a resin column containing a specific type of ion
exchange resin. These ion exchange steps can target the removal of
a specific ion (for example, but not limited to, FE.sup.2+ or
CA.sup.2+) or a broad category of ions (for example, but not
limited to, all anions or all cations). In certain applications, a
mixed bed ion exchange can also be used to remove both anions and
cations within a single process step.
As Ion Exchange sub-process 2380d within third exemplary Ionic
Species Adjustment process 2342d is imagined to be focused on
replacing a first undesired specific ionic species with a second
desired specific ionic species within CNT Formulation 2320, it is
imagined that Anion Exchange sub-process step 2382d uses a resin
column charged with the desired anion 2381d of the second ionic
species to first exchange the undesired anion components 2383d
within CNT Formulation 2320 in a first operation. Subsequently,
Cation Exchange sub-process step 2384d then uses a resin column
charged with the desired cation 2385d of the second ionic species
to exchange the undesired cation components 2387d within CNT
Formulation 2320. As described above, Ion Exchange sub-process
2380d can be performed a single time, as is depicted in FIG. 23D,
or repeated once or more to further exchange more of the desired
ionic species material with the undesired ionic species material
within CNT Formulation 2320. Further, while FIG. 23D depicts Anion
Exchange sub-process step 2382d being performed prior to Cation
Exchange sub-process step 2384d, the methods of the present
disclosure are not limited in this regard. Indeed, as described
above, in certain applications Cation Exchange sub-process step
2384d could be performed prior to Anion Exchange sub-process step
2382d. Further, in certain applications both the cation exchange
and anion exchange sub-process steps could be performed together
using a mixed bed ion exchange process.
Looking now to Crossflow Filtration sub-process 2390d, the ionic
species concentration level of CNT Formulation 2320 is reduced
subsequent to the ionic species exchange operation performed by Ion
Exchange sub-process 2380d. Crossflow Filtration sub-process 2390d
is comprised of a plurality of sub-process steps. CNT Formulation
2320 is first dewatered in sub-process step 2392d such that the CNT
material within the formulation is compacted onto a filtration
membrane in process step 2394d. In this way, a significant volume
of the desired ionic species material present within CNT
Formulation 2320 can be separated from the CNT material, as the
ionic species material passes through the filter membrane while the
CNT material is compacted onto the filter membrane. In a next
sub-process step 2396d, the filtration membrane is purged with
Recovery Solution 2397d. As Crossflow Filtration sub-process 2390d
is intended to reduce the concentration level of ionic species
within CNT Formulation 2320, Recovery Solution 2397d is selected to
be a low-salt containing material, such as, but not limited to,
deionized water. In this way, the compacted CNT material is
recovered back into a formulation with a significantly lower ionic
species concentration as was present within the formulation at the
conclusion of Ion Exchange sub-process 2380d. As described above,
Crossflow Filtration sub-process 2390d can be performed a single
time, as is depicted in FIG. 23D, or repeated once or more to
further reduce the ionic species concentration level present in CNT
Formulation 2320.
In this way, a significant volume (or in, some cases, substantially
all) of an undesired ionic species present in CNT Formulation 2320
can be removed and a desired ionic species added at a selected
concentration level using a combination of an Ion Exchange
sub-process 2380d and a Crossflow Filtration sub-process 2390d,
resulting in Adjusted CNT Formulation 2350, which, within this
particular ionic species adjustment process example 2304, has a
concentration level of desired ionic species set at a desired
target level (as determined by process step 2335 in FIG. 23A).
It should be noted that while third exemplary Ionic Species
Adjustment Process 2342d is depicted as first using an Ion Exchange
sub-process 2380d followed by a subsequent Crossflow Filtration
sub-process 2390d, the methods of the present disclosure are not
limited in this regard. Indeed, in certain applications an ionic
species adjustment process targeted at exchanging one type ionic
species for another within a CNT formulation could include only Ion
Exchange sub-process step 2380d (performed once or multiple times).
Within such applications, Ion Exchange sub-process step 2380d could
be set up, for example, such that the concentration level of the
second ionic species within CNT Formulation 2320 is already at the
target level (as determined by process step 2335 in FIG. 23A) at
the conclusion of the sub-process, and no further concentration
level adjustment required.
FIGS. 23B, 23C, and 23D are provided within the present disclosure
and have been described in detail above in order to illustrate
three different exemplary ionic species concentration adjustment
processes (2302, 2303, and 2304, respectively) suitable for use
within the nanotube fabric formation method detailed within FIG.
23A. Specifically, these three exemplary adjustment processes
(2302, 2303, 2304) are intended as non-limiting examples of process
step 2342 within FIG. 23A. It should be noted that a nanotube
fabric formation process according to the method detailed in FIG.
23A could include one or more of these exemplary ionic species
adjustment processes or variations of these exemplary ionic species
adjustment processes as best befits the needs of a particular
application. It is preferred, therefore, that the present
disclosure not be limited to the specific examples presented
herein.
FIG. 24 is a flow chart detailing a method according to the present
disclosure for generating a nanotube formulation roughness curve
for a particular nanotube formulation with a selected ionic species
(as is required, for example, within process step 2335 of FIG.
23A). In first method step 2410, a CNT Formulation is prepared with
the properties required (e.g., nanotube type, nanotube density,
functionalization parameters, etc.) for a given application,
according to the methods described in detail above (for example,
CNT Formulation 2320 within FIG. 23A). In a next method step 2420,
the type of ionic species to be used to control either or both the
surface roughness of a nanotube fabric or the degree of rafting
within a nanotube fabric formed with this CNT formulation is
selected. As described above (for example, with respect to the
discussion of FIG. 21 above), a plurality of ionic species are well
suited for controlling or otherwise selecting surface roughness
and/or degree of rafting within a nanotube fabric according to the
methods of the present disclosure. As will be described below, the
method of FIG. 24 characterizes this CNT formulation with respect
to the selected ionic species to realize a CNT formulation
roughness curve (for example, 2330 in FIG. 23A) for the particular
CNT formulation and ionic species that can be used to select a
concentration level of the ionic species within the CNT formulation
to realize a nanotube fabric with desired surface roughness and
degree of rafting properties.
Within next method step 2430, a plurality of test ionic species
concentration levels are selected to test. As described within the
discussion of FIG. 22, these test concentration levels will be used
to generate data points to form the nanotube formulation roughness
curve. The test concentration levels should be selected to provide
a range of surface roughness values and degrees of rafting within
nanotube fabrics formed from CNT formulations using the test ionic
species concentration values. Within the exemplary nanotube
formulation roughness curves of FIGS. 26A-26D, four test ionic
species concentration levels were used to generate four data points
to define the curves (e.g., 2210 in FIG. 22). However, the methods
of the present disclosure are not limited in this regard. Indeed,
any number of data points can be used to produce a nanotube
formulation roughness curve, including, but not limited to, 2, 3,
4, 5, 10, 15, 20, 50, or 100. This is to say, the number of data
points generated and used to create a nanotube formulation
roughness curve is only limited by the specific needs of an
application.
Within next method step 2440, the CNT Formulation prepared in
method step 2410 is used to produce a plurality of identical test
samples for each of the test ionic species concentration levels
selected in method step 2430. In next method step 2850, the
concentration level of the selected ionic species (selected in
method step 2420) within each of the CNT Formulation test samples
is adjusted--using, for example, the methods described in detail
within FIGS. 23A-23D above--to one of the ionic species
concentration test levels selected in method step 2430. In this
way, a plurality of CNT formulations is created, with each CNT
formulation exhibiting a different ionic species concentration
level according to plurality of test ionic species concentration
levels selected in method step 2430.
In next method step 2460, each of the adjusted CNT formulation
samples is deposited (by, for example, a spin coating operation) to
form a test sample nanotube fabric for each of the plurality of
test ionic species concentration levels selected in method step
2430. Methods for forming nanotube fabrics from CNT formulations
have been described in detail above and are also disclosed in more
detail within the incorporated references. In next method step
2870, each of the test sample nanotube fabrics is analyzed to
quantify both the surface roughness of the fabric (measured as the
RMS roughness within examples 10-23) and degree of rafting
(measured as the standard deviation of the positional orientation
of nanotube elements within examples 10-23). Within next method
step 2480, these measured values (each set associated with one of
the plurality of ionic species concentration levels selected in
method step 2430) are used to generate a nanotube formulation
roughness curve, as described within the discussion of FIG. 22
above. As discussed in detail above, according to the methods of
the present disclosure, this nanotube formulation roughness curve
can then be used to define a utilizable range corresponding to a
desired set of parameters (with respect to surface roughness and
degree of rafting) within a nanotube fabric, and this utilizable
range then used to aid in the selection of a target ionic species
concentration level to be used within a nanotube fabric formation
process (e.g., FIG. 23A).
Within method step 2470 of FIG. 24, the surface roughness of a
plurality of test nanotube fabrics is quantified. Within examples
10-23 of the present disclosure (discussed in detail below), an
image analysis tool (Gwyddion version 2.50) was used to analyze AFM
images of the sample nanotube fabrics generated. Gwyddion is a
modular program (available online at the time of the writing of
this disclosure) for SPM (scanning probe microscopy) data
visualization and analysis and is primarily intended for the
analysis of height fields obtained by scanning probe microscopy
techniques. Within examples 10-23, the AFM images were collected
using a Veeco Instruments, Inc. D3100 AFM using a Nanosensors.TM.
PointProbe.RTM. Plus Non-Contact/Tapping Mode--High Resonance
Frequency (PPP-NHC) probe with a scan size of 2.5 um with 512
points per line in tapping mode. The directionality measurements
within examples 10-23 were performed using similar visual analysis
tools on SEM images of sample nanotube fabrics. For these
directionality measurements, an FEI XL30 TMP scanning electron
microscope was used to collect images at 10 kV with a spot size of
3 and a working distance of 5 mm.
It should be noted that a plurality of analysis tools and
techniques are presently available for analyzing and quantifying
the roughness or smoothness of a material layer at a nanoscopic
level (that is, on the order of a nanometer) as well as for
analyzing the directionality of high aspect ratio nanoscopic
elements within a material layer. Such tools and techniques are
well known to those skilled in the art. It is preferred, therefore,
that the methods of the present disclosure not be limited to the
particular analysis and quantification methods/tools used within
the examples of the present disclosure with respect to method step
2470 of FIG. 24, as these methods and tools are intended purely as
non-limiting examples.
FIG. 25 is a table 2500 summarizing the data and results presented
in examples 10-23, with each row listing the parameters used for
and results taken from each example, as indicated in the first
column ("Example #"). Within each of examples 10-23, a sample
nanotube fabric was formed using the method detailed in FIG. 23A in
order to provide data points for at least one of four nanotube
fabric roughness curve (FIGS. 26A-26D) according to the method of
FIG. 24. The particular CNT formulation, type of ionic species, and
the ionic species concentration level used within each example is
listed within the second, third, and fourth columns of table 2500,
respectively. Further, for the resulting nanotube fabric of each
example, the RMS surface roughness and the standard deviation of
the positional orientation of the nanotube elements within the
fabric (indicative of the degree of rafting within the fabric) are
listed in the fifth and sixth columns of table 2500, respectively.
Finally, the relevant figures documenting the test data produced
within each example are listed in the seventh column of table
2500.
As summarized in table 2500, within examples 10-23, two nanotube
formulations were used ("B" and "C"), each with two types of ionic
species (ammonium nitrate and tetramethyl ammonium formate) to form
a plurality of sample nanotube fabrics which were used to realize
four different nanotube fabric roughness curves (FIGS. 26A-26D). As
will be discussed below, FIG. 26A is a nanotube fabric roughness
curve 2610 which corresponds to nanotube formulation "B" for
concentrations of ammonium nitrate (NH.sub.4NO.sub.3). FIG. 26B is
a nanotube fabric roughness curve 2620 which corresponds to
nanotube formulation "B" for concentrations of tetramethyl ammonium
formate (TMA Fm). FIG. 26C is a nanotube fabric roughness curve
2630 which corresponds to nanotube formulation "C" for
concentrations of ammonium nitrate (NH.sub.4NO.sub.3). FIG. 26D is
a nanotube fabric roughness curve 2640 which corresponds to
nanotube formulation "C" for concentrations of tetramethyl ammonium
formate (TMA Fm).
The nanotube elements used within nanotube formulation "B" (used in
examples 10-16) were predominately multi-walled carbon nanotubes,
which had a significant plurality of kinks and bends and exhibited
a median length of 132 nm and a 95th percentile length of 260 nm.
The nanotube elements used within nanotube formulation "C" (used in
examples 17-23) were predominately singled walled carbon nanotubes,
which were relatively straight (that is, have few bends of kinks)
and exhibited a median length of 187 nm and a 95th percentile
length of 494 nm. Examples of nanotube elements used within
nanotube formulation "B" are shown in the TEM images of FIGS. 20C
and 20D and discussed above within the discussion of those figures.
Examples of nanotube elements used within nanotube formulation "C"
are shown in the TEM images of FIGS. 20E and 20F and discussed
above within the discussion of those figures.
Both nanotube formulation "B" and nanotube formulation "C" were
first realized through the following method. Fifty grams of raw
(that is, unfunctionalized) carbon nanotubes (CNTs) of the selected
type (as discussed above) were refluxed in microelectronics grade
nitric acid. Supplies of raw nanotubes (such as were used in the
examples of the present disclosure and depicted in FIGS. 20A-20E)
may be purchased commercially from a number of vendors (e.g.,
Thomas Swan, Nano-C, and Zeon Corporation). The concentration of
the nitric acid, the reflux time, and temperature were optimized
based on the starting CNT material. For example, CNTs were refluxed
in concentrated nitric acid (40%) at 120.degree. C. for 4-14 hours.
After the nitric acid reflux step, the CNT suspension in acid was
diluted in 0.35 to 3% nitric acid solution (8-16 L) and taken
through several passes of cross-flow filtration (CFF). First few
passes of CFF (hereinafter called CFF1) may remove the acid and
soluble metal salts in the suspension. The pH of the suspension
during the CFF1 steps was maintained at 1+/-0.3 by recovering the
material in 0.35-3% nitric acid after each step. Typically, five to
eleven CFF1 steps were performed. After the CFF1 steps, the
retentate was collected in DI water and the pH of the nanotube:DI
water suspension was increased to 8+/-0.2 with ammonium hydroxide
(concentration 29%) and sonicated. This liquid was taken through
another set of CFF passes (hereinafter referred as CFF2). CFF2 may
remove the amorphous carbon impurities in the solution. After the
CFF2 process, the retentate was collected in DI water and the pH of
the nanotube:DI water liquid was adjusted to pH 8+/-0.2 and the
solution was sonicated for 120 minutes in a chilled sonicator bath
(4-5.degree. C.).
At this step of the process a desired concentration or optical
density of the CNT formulation can be achieved by controlling the
volume of the DI water used to recover the retentate from the CFF2
membrane. For example if the optical density of the CNT formulation
before the last CFF2 step is 2 and the volume is 2 L, then a
recovery volume of 1 L can lead to an optical density close to 4
assuming there is negligible loss in optical density through the
permeate at this point. Similarly, if the optical density of the
CNT formulation before the last CFF2 step is 2 and the volume is 16
L, then a recovery volume of 1 L can lead to a CNT formulation of
optical density 32. The concentration of the CNT formulation
(optical density) that can be practically achieved is dependent on,
but is not limited to, the starting CNT charge used in the
reaction, the reaction conditions, number of CFF steps, CFF
membrane pore size, CFF membrane surface area, and pH.
Finally, the formulation was centrifuged two or three times at
about 70000-100000 g for about 20-30 min each. In certain cases,
the pH of the formulation was adjusted to 8+/-0.2 in between the
centrifugation passes which may remove residual metal or carbon
nanoparticles in the liquid by sedimentation. After the
centrifugation step, the supernatant was collected and used as the
final purified nanotube formulation. The concentration of the final
nanotube application solution depends on the centrifugation
conditions used. Typically for a spin coat application, CNT
solutions with an optical density of 10-100 measured at 550 nm
wavelength and a pH of 7+/-0.5 were used.
Further, within examples 11-16 and 18-23 and, a selected ionic
species (ammonium nitrate for examples 11-13 and 18-20, and
tetramethyl ammonium formate for examples 14-16 and 21-23) was
introduced to the purified nanotube formulation, and the
concentration level of the selected ionic species adjusted (as
described within the discussion of FIGS. 23A-23D, above) to the
selected test concentration level for each example. Within examples
10 and 17, the ionic species concentration was selected to be
essentially zero. Within each example, the adjusted nanotube
formulation was then spun coat over a silicon dioxide substrate to
form a nanotube fabric layer, approximately 20 nm thick.
Specifically, four spin coating operations were performed to form
the nanotube fabric layers of examples 10-16, and three spin
coating operation were performed to form the nanotube fabric layers
of examples 17-23.
For all operations, the spin coating operations were as follows. A
raw wafer was pre-baked on a 250.degree. C. hot plate for five
minutes. After cooling, the wafer was placed in spin-coat tool and
underwent a pre-wet step where approximately 3 mL of de-ionized
water was dispensed onto the wafer, and then spun for approximately
3 s and slung off at 280 rpm. After this pre-wet step,
approximately 3 ml of the adjusted solution was dispensed onto the
wafer while the wafer was rotated at 60 rpm. Following this
solution dispensing step, the wafer then went through a series of
steps with various spin speeds (35-180 rpm) to ensure the solution
was spread evenly across the wafer during the spin coat process.
Finally, the spin speed was increased up to 2000 rpm for ten
seconds. The wafer was placed on a 250.degree. C. hot plate for
three and a half minutes between each spin coating operation. After
a cool down cycle, the entire process was repeated such as to apply
the desired number of coats of the application solution over the
wafer.
FIG. 26A shows a nanotube formulation roughness curve 2610
according to the methods of the present disclosure corresponding to
nanotube formulation "B" (as defined above) used with ammonium
nitrate (NH.sub.4NO.sub.3) as an ionic species. The curve shown in
nanotube formulation roughness curve 2610 is drawn through four
data points: 2612 provided by example 10, 2614 provided by example
11, 2616 provided by example 12, and 2618 provided by example 13.
As described above with respect to FIG. 22, a utilization range
2619 is drawn to indicate the range of ionic species concentrations
(approximately 0.4 mM-1.1 mM) that will provide a nanotube fabric
within the given parameters of an exemplary application used
herein. For the nanotube formulation roughness curve 2610 of FIG.
26A, the parameters of this exemplary application are imagined to
be a nanotube fabric with an RMS roughness of less than 2.8 nm and
a standard deviation of orientation of approximately 20.degree. or
higher (representative of a substantially low degree of
rafting).
FIG. 26B shows a nanotube formulation roughness curve 2620
according to the methods of the present disclosure corresponding to
nanotube formulation "B" (as defined above) used with tetramethyl
ammonium formate (TMA Fm) as an ionic species. The curve shown in
nanotube formulation roughness curve 2620 is drawn through four
data points: 2622 provided by example 10, 2624 provided by example
14, 2626 provided by example 15, and 2628 provided by example 16.
As described above with respect to FIG. 22, a utilization range
2629 is drawn to indicate the range of ionic species concentrations
(approximately 0.4 mM-1.5 mM) that will provide a nanotube fabric
within the given parameters of an exemplary application used
herein. For the nanotube formulation roughness curve 2620 of FIG.
26B, the parameters of this exemplary application are imagined to
be a nanotube fabric with an RMS roughness of less than 2.2 nm and
a standard deviation of orientation of approximately 27.degree. or
higher (representative of a substantially low degree of
rafting).
FIG. 26C shows a nanotube formulation roughness curve 2630
according to the methods of the present disclosure corresponding to
nanotube formulation "C" (as defined above) used with ammonium
nitrate (NH.sub.4NO.sub.3) as an ionic species. The curve shown in
nanotube formulation roughness curve 2630 is drawn through four
data points: 2632 provided by example 17, 2634 provided by example
18, 2636 provided by example 19, and 2638 provided by example 20.
As described above with respect to FIG. 22, a utilization range
2639 is drawn to indicate the range of ionic species concentrations
(approximately 0.1 mM-0.6 mM) that will provide a nanotube fabric
within the given parameters of an exemplary application used
herein. For the nanotube formulation roughness curve 2630 of FIG.
26C, the parameters of this exemplary application are imagined to
be a nanotube fabric with an RMS roughness of less than 3.1 nm and
a standard deviation of orientation of approximately 26.degree. or
higher (representative of a substantially low degree of
rafting).
FIG. 26D shows a nanotube formulation roughness curve 2640
according to the methods of the present disclosure corresponding to
nanotube formulation "C" (as defined above) used with tetramethyl
ammonium formate (TMA Fm) as an ionic species. The curve shown in
nanotube formulation roughness curve 2640 is drawn through four
data points: 2642 provided by example 17, 2644 provided by example
21, 2646 provided by example 22, and 2648 provided by example 23.
As described above with respect to FIG. 22, a utilization range
2649 is drawn to indicate the range of ionic species concentrations
(approximately 0.1 mM-1.0 mM) that will provide a nanotube fabric
within the given parameters of an exemplary application used
herein. For the nanotube formulation roughness curve 2640 of FIG.
26D, the parameters of this exemplary application are imagined to
be a nanotube fabric with an RMS roughness of less than 2.4 nm and
a standard deviation of orientation of approximately 27.degree. or
higher (representative of a substantially low degree of
rafting).
FIG. 27 is a diagram illustrating a material layer height mapping
method used to illustrate the surface roughness of nanotube fabrics
formed within examples 10-23. This material layer height mapping
method was used to produce FIGS. 28B, 29B, 30B, 31B, 32B, 33B, 34B,
35B, 36B, 37B, 38B, 39B, 40B, and 41B, which graphically illustrate
a topographical view of AFM images taken of the nanotube fabrics in
each of examples 10-23. As described above with respect to method
step 2470 of FIG. 24, an AFM image was produced for each of the
nanotube fabrics formed in examples 10-23. These AFM images were
then visually analyzed, as described above, to realize a
512.times.512 table of numerical height values for the nanotube
fabric surface. The material layer height mapping method
illustrated in FIG. 27 then reduced this 512.times.512 table of
height values to a 128.times.128 table of height values by first
organizing the values with the 512.times.512 table into 4 element
(2.times.2) groups, averaging the four values within each group,
then using that average value to represent the four original
elements. Each of these averaged values was then quantized (as
illustrated in FIG. 27) and assigned a 4.times.4 pixel tile
2730a-2730f. These 4.times.4 pixel tiles 2730a-2730f were then
plotted to graphically represent the surface of each nanotube
fabric (e.g., FIG. 28B).
Within FIG. 27, a contoured material layer 2710 is used represent
the sample nanotube fabrics of examples 10-23. Measuring ruler 2720
is used to the indicate the height of the material surface 2710a
falls above or below nominal surface plane (analogous to horizontal
surface line 1830 and horizontal surface line 1930 in FIGS. 18B and
19B, discussed above). This ruler is then used to generate
quantization tile map 2730. Within examples 10-23, a range of +/-20
nm above or below the nominal surface plane of the fabric was
sufficient to include all of the values measured from the AFM
images produced. As such, eight tiles 2720a-2730f were used to
represent 5 nm ranges between -20 nm and 20 nm, as indicated in
FIG. 27. In this way, a black line plot that was visually
representative of the nanotube fabric surfaces could be realized in
order to illustrate differing surface textures of nanotube fabrics
within the present disclosure.
It should be noted that the height mapped topographical images of
FIGS. 28B, 29B, 30B, 31B, 32B, 33B, 34B, 35B, 36B, 37B, 38B, 39B,
40B, and 41B are intended for visual illustration of comparative
nanotube fabric surface textures within the present disclosure
only. The RMS roughness measurements within examples 10-23
(summarized within the fifth column of table 2500 in FIG. 25, and
used to produce nanotube fabric roughness curves 2610, 2620, 2630,
and 2640 in FIGS. 26A, 26B, 26C, and 26D, respectively) were all
calculated from visual analysis of the 512.times.512 AFM images
produced for each of the nanotube fabrics within those examples, as
is explained in detail with respect above with respect to method
step 2870 of FIG. 24.
Example 10
FIGS. 28A-28C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 10. The nanotube fabric of example
10 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ionic species concentration level of
substantially zero (as described in detail with respect to FIGS.
23A-23D above), then performing four spin coating operations of the
adjusted nanotube formulation over a silicon wafer (again, as
described in detail above) to form a nanotube fabric approximately
20 nm thick. FIG. 28A is an SEM image 2801 illustrating the
resulting nanotube fabric, FIG. 28B is a topographical plot 2802 of
the surface of the resulting nanotube fabric, and FIG. 28C is a
normalized histogram 2803 plotting the positional orientation
frequency of the nanotube elements as shown within SEM image 2801.
As listed in FIG. 25, the nanotube fabric formed within example 10
has an RMS roughness of 1.72 nm and the standard deviation of the
nanotube positional orientation within the fabric was approximately
14.degree. (indicating moderate rafting within the fabric). The
measurements from this fabric, formed from nanotube formulation "B"
with essentially no ionic species present within the formulation,
were used to provide data point 2612 in FIG. 26A and 2622 in FIG.
26B.
Example 11
FIGS. 29A-29C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 11. The nanotube fabric of example
11 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ammonium nitrate (NH.sub.4NO.sub.3)
concentration level of approximately 0.75 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing four
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 29A is an SEM image
2901 illustrating the resulting nanotube fabric, FIG. 29B is a
topographical plot 2902 of the surface of the resulting nanotube
fabric, and FIG. 29C is a normalized histogram 2903 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 2901. As listed in FIG. 25, the nanotube fabric
formed within example 11 has an RMS roughness of 2.36 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 27.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "B" with an ammonium
nitrate (NH.sub.4NO.sub.3) concentration level of approximately
0.75 mM, were used to provide data point 2614 in FIG. 26A.
Example 12
FIGS. 30A-30C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 12. The nanotube fabric of example
12 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ammonium nitrate (NH.sub.4NO.sub.3)
concentration level of approximately 1.50 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing four
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 30A is an SEM image
3001 illustrating the resulting nanotube fabric, FIG. 30B is a
topographical plot 3002 of the surface of the resulting nanotube
fabric, and FIG. 30C is a normalized histogram 3003 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3001. As listed in FIG. 25, the nanotube fabric
formed within example 12 has an RMS roughness of 3.04 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 25.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "B" with an ammonium
nitrate (NH.sub.4NO.sub.3) concentration level of approximately
1.50 mM, were used to provide data point 2616 in FIG. 26A.
Example 13
FIGS. 31A-31C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 13. The nanotube fabric of example
13 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ammonium nitrate (NH.sub.4NO.sub.3)
concentration level of approximately 7.50 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing four
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 31A is an SEM image
3101 illustrating the resulting nanotube fabric, FIG. 31B is a
topographical plot 3102 of the surface of the resulting nanotube
fabric, and FIG. 31C is a normalized histogram 3103 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3001. As listed in FIG. 25, the nanotube fabric
formed within example 13 has an RMS roughness of 4.10 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 31.degree. (indicating a low degree of
rafting within the fabric). The measurements from this fabric,
formed from nanotube formulation "B" with an ammonium nitrate
(NH.sub.4NO.sub.3) concentration level of approximately 7.50 mM,
were used to provide data point 2618 in FIG. 26A.
Example 14
FIGS. 32A-32C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 14. The nanotube fabric of example
14 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have a tetramethyl ammonium formate (TMA Fm)
concentration level of approximately 0.75 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing four
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 32A is an SEM image
3201 illustrating the resulting nanotube fabric, FIG. 32B is a
topographical plot 3202 of the surface of the resulting nanotube
fabric, and FIG. 32C is a normalized histogram 3203 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3201. As listed in FIG. 25, the nanotube fabric
formed within example 14 has an RMS roughness of 1.95 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 29.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "B" with a
tetramethyl ammonium formate (TMA Fm) concentration level of
approximately 0.75 mM, were used to provide data point 2624 in FIG.
26B.
Example 15
FIGS. 33A-33C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 15. The nanotube fabric of example
15 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have a tetramethyl ammonium formate (TMA Fm)
concentration level of approximately 1.50 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing four
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 33A is an SEM image
3301 illustrating the resulting nanotube fabric, FIG. 33B is a
topographical plot 3302 of the surface of the resulting nanotube
fabric, and FIG. 33C is a normalized histogram 3303 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3301. As listed in FIG. 25, the nanotube fabric
formed within example 15 has an RMS roughness of 2.22 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 28.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "B" with a
tetramethyl ammonium formate (TMA Fm) concentration level of
approximately 1.50 mM, were used to provide data point 2626 in FIG.
26B.
Example 16
FIGS. 34A-34C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 16. The nanotube fabric of example
16 was formed by taking a sample of nanotube formulation "B"
(formulated as described in detail above), adjusting the nanotube
formulation to have a tetramethyl ammonium formate (TMA Fm)
concentration level of approximately 7.50 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing four
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 34A is an SEM image
3401 illustrating the resulting nanotube fabric, FIG. 34B is a
topographical plot 3402 of the surface of the resulting nanotube
fabric, and FIG. 34C is a normalized histogram 3403 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3401. As listed in FIG. 25, the nanotube fabric
formed within example 16 has an RMS roughness of 2.61 nm and the
standard deviation of the nanotube positional orientation within
the fabric was essentially undefined (indicating a essentially no
rafting within the fabric). The measurements from this fabric,
formed from nanotube formulation "B" with a tetramethyl ammonium
formate (TMA Fm) concentration level of approximately 7.50 mM, were
used to provide data point 2628 in FIG. 26B.
Example 17
FIGS. 35A-35C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 17. The nanotube fabric of example
17 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ionic species concentration level of
substantially zero (as described in detail with respect to FIGS.
23A-23D above), then performing three spin coating operations of
the adjusted nanotube formulation over a silicon wafer (again, as
described in detail above) to form a nanotube fabric approximately
20 nm thick. FIG. 35A is an SEM image 3501 illustrating the
resulting nanotube fabric, FIG. 35B is a topographical plot 3502 of
the surface of the resulting nanotube fabric, and FIG. 35C is a
normalized histogram 3503 plotting the positional orientation
frequency of the nanotube elements as shown within SEM image 3501.
As listed in FIG. 25, the nanotube fabric formed within example 17
has an RMS roughness of 1.77 nm and the standard deviation of the
nanotube positional orientation within the fabric was approximately
25.degree. (indicating a moderate low degree of rafting within the
fabric). The measurements from this fabric, formed from nanotube
formulation "C" with essentially no ionic species present within
the formulation, were used to provide data point 2632 in FIG. 26C
and 2642 in FIG. 26D.
Example 18
FIGS. 36A-36C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 18. The nanotube fabric of example
18 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ammonium nitrate (NH.sub.4NO.sub.3)
concentration level of approximately 0.71 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing three
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 36A is an SEM image
3601 illustrating the resulting nanotube fabric, FIG. 36B is a
topographical plot 3602 of the surface of the resulting nanotube
fabric, and FIG. 36C is a normalized histogram 3603 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3601. As listed in FIG. 25, the nanotube fabric
formed within example 18 has an RMS roughness of 3.22 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 28.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "C" with an ammonium
nitrate (NH.sub.4NO.sub.3) concentration level of approximately
0.71 mM, were used to provide data point 2634 in FIG. 26C.
Example 19
FIGS. 37A-37C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 19. The nanotube fabric of example
19 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ammonium nitrate (NH.sub.4NO.sub.3)
concentration level of approximately 1.43 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing three
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 37A is an SEM image
3701 illustrating the resulting nanotube fabric, FIG. 37B is a
topographical plot 3702 of the surface of the resulting nanotube
fabric, and FIG. 37C is a normalized histogram 3703 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3701. As listed in FIG. 25, the nanotube fabric
formed within example 19 has an RMS roughness of 3.62 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 28.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "C" with an ammonium
nitrate (NH.sub.4NO.sub.3) concentration level of approximately
1.43 mM, were used to provide data point 2636 in FIG. 26C.
Example 20
FIGS. 38A-38C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 20. The nanotube fabric of example
20 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have an ammonium nitrate (NH.sub.4NO.sub.3)
concentration level of approximately 8.14 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing three
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 38A is an SEM image
3801 illustrating the resulting nanotube fabric, FIG. 38B is a
topographical plot 3802 of the surface of the resulting nanotube
fabric, and FIG. 38C is a normalized histogram 3803 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3801. As listed in FIG. 25, the nanotube fabric
formed within example 20 has an RMS roughness of 3.82 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 28.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "C" with an ammonium
nitrate (NH.sub.4NO.sub.3) concentration level of approximately
8.14 mM, were used to provide data point 2638 in FIG. 26C.
Example 21
FIGS. 39A-39C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 21. The nanotube fabric of example
21 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have a tetramethyl ammonium formate (TMA Fm)
concentration level of approximately 0.75 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing three
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 39A is an SEM image
3901 illustrating the resulting nanotube fabric, FIG. 39B is a
topographical plot 3902 of the surface of the resulting nanotube
fabric, and FIG. 39C is a normalized histogram 3903 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 3901. As listed in FIG. 25, the nanotube fabric
formed within example 21 has an RMS roughness of 2.33 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 34.degree. (indicating a low degree of
rafting within the fabric). The measurements from this fabric,
formed from nanotube formulation "C" with a tetramethyl ammonium
formate (TMA Fm) concentration level of approximately 0.75 mM, were
used to provide data point 2644 in FIG. 26D.
Example 22
FIGS. 40A-40C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 22. The nanotube fabric of example
22 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have a tetramethyl ammonium formate (TMA Fm)
concentration level of approximately 1.50 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing three
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 40A is an SEM image
4001 illustrating the resulting nanotube fabric, FIG. 40B is a
topographical plot 4002 of the surface of the resulting nanotube
fabric, and FIG. 40C is a normalized histogram 4003 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 4001. As listed in FIG. 25, the nanotube fabric
formed within example 22 has an RMS roughness of 2.50 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 30.degree. (indicating a low degree of
rafting within the fabric). The measurements from this fabric,
formed from nanotube formulation "C" with a tetramethyl ammonium
formate (TMA Fm) concentration level of approximately 1.50 mM, were
used to provide data point 2646 in FIG. 26D.
Example 23
FIGS. 41A-41C illustrate the surface roughness and degree of
rafting within a nanotube fabric produced using the methods of the
present disclosure (as described in detail above) in accordance
with the parameters of example 23. The nanotube fabric of example
23 was formed by taking a sample of nanotube formulation "C"
(formulated as described in detail above), adjusting the nanotube
formulation to have a tetramethyl ammonium formate (TMA Fm)
concentration level of approximately 7.50 mM (as described in
detail with respect to FIGS. 23A-23D above), then performing three
spin coating operations of the adjusted nanotube formulation over a
silicon wafer (again, as described in detail above) to form a
nanotube fabric approximately 20 nm thick. FIG. 41A is an SEM image
4101 illustrating the resulting nanotube fabric, FIG. 41B is a
topographical plot 4102 of the surface of the resulting nanotube
fabric, and FIG. 41C is a normalized histogram 4103 plotting the
positional orientation frequency of the nanotube elements as shown
within SEM image 4101. As listed in FIG. 25, the nanotube fabric
formed within example 23 has an RMS roughness of 2.78 nm and the
standard deviation of the nanotube positional orientation within
the fabric was approximately 28.degree. (indicating a moderately
low degree of rafting within the fabric). The measurements from
this fabric, formed from nanotube formulation "C" with a
tetramethyl ammonium formate (TMA Fm) concentration level of
approximately 7.50 mM, were used to provide data point 2648 in FIG.
26D.
Although the present invention has been described in relation to
particular embodiments thereof, many other variations and
modifications and other uses will become apparent to those skilled
in the art. It is preferred, therefore, that the present invention
not be limited by the specific disclosure herein, but rather be
defined by the appended claims; and that these claims will
encompass modifications of and improvements to what has been
described.
* * * * *